Integrated Traffic Management at Junction 33 of the M1 Evaluation Report
Integrated Traffic Management at Junction 33 of the M1
Evaluation Report
JOB NUMBER: 5035805 DOCUMENT REF: 5035805 04 02 022 Evaluation Report.
03 Initial Issue KA Butler JJ Steed SR Fradd JJ Steed July 08
02 Draft for HA Approval KA Butler - JJ Steed JJ Steed June 08
01 Draft for HA Comment KA Butler A Maher / PA JJ Steed JJ Steed May 08 Leach
Originated Checked Reviewed Authorised Date
Revision Purpose Description
INTEGRATED TRAFFIC MANAGEMENT AT JUNCTION 33 OF THE M1
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Contents
Section Page
Executive Summary iv 1. Introduction 1 1.1 Evaluation Area 2 1.2 Evaluation Goals and Aims 2 1.3 Evaluation Scenarios 3 2. Evaluation Method 5 2.1 Periodicity and Data Selection 5 2.2 Motorway (MIDAS) Data 6 2.3 Journey Time Data 7 2.4 Automatic Traffic Counter (ATC) Data 9 2.5 Ramp Metering and Traffic Controller Data 10 2.6 Incident and Weather Data 10 2.7 Incident Data 10 2.8 HANET data 11 3. Relevant Events and Evaluation Timeline 12 3.1 Major and Long-term Events during ITM Evaluation 12 3.2 Evaluation Timeline 13 4. Data Analysis - ITM Activation 15 4.1 Traffic Trends in Evaluation Area 15 4.2 Journey Time through Junction 33 15 4.3 Volume on the Local Road Network 18 4.4 Journey Time Data 18 4.5 Impact of ITM on the Motorway Southbound Carriageway 26 4.6 Improvements to the Mainline Flow 28 4.7 Cost Benefit Analysis 29 4.8 Benefits 31 5. Conclusions 34 5.1 Introduction 34 5.2 Journey Time Savings 34 5.3 Stakeholder Involvement 35 5.4 Technology 35
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5.5 Recommendation 36 Glossary 37 Appendix A – Statistical Tools 38 Appendix B – ATC Volume Charts 44 Appendix C – Journey Time Histograms 49 Appendix D – Traffic Signal Controller Configuration 78 Appendix E – Scenario A Traffic Trends 81 Appendix F - Lessons Learnt Report 89 1. Introduction 89 1.1 Purpose 89 1.2 Governance 89 1.3 Background 89 2. Lessons Learnt 90 2.1 The Steering Group 90 2.2 Project Issues 90
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List of Tables Table 2.1 – ANPR Link Details 7 Table 2.2 – Implications of Parameter Value Change for Journey Times 9 Table 3.1 – Evaluation Timeline 14 Table 4.1 – Journey Time Analysis 20 Table 4.2 – Weighted Averages 24 Table 4.3 – Ramp Metering Evaluation Results 27 Table 4.4 – ITM Costs 30 Table 4.5 – Indicative Benefits 32
List of Figures Figure 1.1 – ITM Evaluation Area 2 Figure 2.1 – Data Validity Flow Diagram 6 Figure 2.2 – ANPR Camera Locations 7 Figure 2.3 – ATC Locations 9 Figure 3.1 – ITM Project Timeline 13 Figure 4.1 – Comparison of Average Journey Time Northbound 16 Figure 4.2 – Comparison of Average Journey Time Southbound 17
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Executive Summary
Integrated Traffic Management (ITM) requires the commitment of both the local authorities and the Highways Agency to seek improvements in traffic management at the boundary of the motorway and the all-purpose road network. The technical approach integrates the operation of ramp metering with the operation of the adjacent traffic signal controller to better manage the combined network. However, ITM also includes other improvements delivered through a combined and equitable approach to network improvement by all parties As such, integration applies not only to the technical aspects of the project but the institutional integration necessary to achieve the desired objective.
The holistic approach to implementing ITM at a pilot site, Junction 33 of the M1 near Sheffield and Rotherham has been successful. Benefits have been demonstrated on both the motorway and local road network.
Critical to the successful operation of ramp metering is the management of the queues generated on the slip road. Local authorities are naturally concerned that queues should not extend beyond the end of the slip road. At Junction 33, the traffic signals were configured to operate more efficiently and also to respond to data messages derived at the ramp metering controller indicating the extent of measured queue lengths on the metered slip road. The practical application of ITM is to adjust incrementally the flow arrival rate of traffic at the slip road to manageable platoon sizes. Ramp metering only operates in the evening peak period when it is needed but improvements to the local signals provide benefits throughout the day.
Ramp metering was installed on the southbound motorway entry slip road of the M1 at Junction 33 in early 2007. In an independent evaluation1 of ramp metering operation in September 2007, journey times on the southbound motorway carriageway improved with a saving in evening peak journey times of 9.1%. This benefit was reassessed following ITM switch-on and the measured journey time saving was 14.7% compared to the state before ramp metering was introduced. Whilst some of this benefit may be attributed to ITM, some of the measured benefit could be attributed to other changes in the motorway network.
Journey times on the local road network have decreased since the introduction of ITM. The overall weighted average journey time saving over a 24 hour period for traffic on the local road network was 8.7%. During the peak evening period when ramp metering and ITM were operating, this figure improves the journey time saving to 9.8%.
These results indicate that the local roads and the motorway traffic both benefit from the introduction of ITM. One would expect an element of queue redistribution and thus some delay penalty to one type of user over the other. The positive results may be explained by the considerable effort that went into validating the traffic signals and recalibrating the ramp metering to allow for the introduction of the ITM link between the two systems. Improvements in these individual systems have attributed to much of the benefit measured.
The ITM approach of cooperative working also delivered a number of other qualitative benefits such as an improved maintenance regime; improved road markings; and, a legacy from the evaluation exercise of permanent real time motorway data and video surveillance of
1 “Ramp Metering Operational Assessment” March 2008, Atkins document number 5063147_04_02_027 Issue 4
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the junction available to the local authority. Other improvements are planned to use this data to influence traffic flows further from the immediate network around Junction 33.
The original intention of the pilot was to evaluate ITM with MOVA, a dynamic traffic control strategy. However, protracted local planning issues outside the control of this project precluded this. Had the traffic signal controller been operating MOVA, the traffic arrival rate at the metered stop line would tend to be more variable. Fixed time plans operating at Junction 33, do not allow sufficient variability for the ITM control loop to influence the behaviour of the signals in the same way that might be expected if a more variable traffic control strategy were operating. It is therefore a recommendation of this report that ITM should be trialled on a similar network operating the dynamic traffic signal control strategy.
During the course of the project great emphasis was placed on cooperative working between the various stakeholders which as a whole has contributed to the success of the ITM Pilot Project.
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1. Introduction
The primary objectives of the Highways Agency and the other highway authorities often conflict. The Agency aims to provide an efficient highway network for longer distance travellers and freight whilst the local authorities look to cater for local residents and businesses. This conflict of interest is most apparent at the interface of the two networks.
A range of traffic management techniques are used to optimise the capacity of the strategic network. One such technique is ramp metering. By metering the rate at which traffic joins the main carriageway from a slip road at a junction the mainline flow remains stable and less congested. Whilst there is a slight additional delay to traffic on the slip road itself, this is more than offset by the maintenance of steady and stable traffic flows achieved on the main carriageway2. This consequently provides benefits to both the strategic and local road networks. However, the success of ramp metering is sometimes limited by the capacity of the slip road to ‘store’ the metered traffic
Integrated Traffic Management (ITM) seeks to address this issue by:
“the integrated application of existing traffic management techniques on national strategic routes and the associated network corridor of adjacent roads and interchanges to manage access to, and from, the strategic route network by optimising vehicle delay in the combined strategic and local road network”.3
ITM, as implemented at M1 Junction 33, has sought to integrate the traffic signal control of the all-purpose network directly to the ramp metering of the southbound access slip road to the M1 main carriageway. At its inception, ITM was expected to provide additional ‘storage’ capacity at the junction to enable the more efficient use of ramp metering. However, it was feared that it might also have an overall detrimental impact upon all-purpose through traffic at the junction. As part of the pilot, real time data from the site is available to the local urban traffic control centre to influence other traffic management and information systems. There are plans to provide traveller information, using a variable message sign (VMS), on the approach to the motorway linked to the operation of the systems at the junction. This will be installed at a key decision point on the all-purpose network to advise travellers about the operational state of the M1. This had not been implemented at the time of writing this report.
This evaluation report assesses the impact of the ITM on the traffic at M1 Junction 33 and the overall management performance and relationships amongst the various organisations directly involved in the scheme.
2 Ramp Metering Evaluation Report, March 2008, Atkins Document number 5053147_04_02_027 3 ITM Final [Feasibility] Report, Motorway Access Management Project, 5032714, Document 001_0072_T_554.doc, April 2006
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The pilot scheme has been implemented and evaluated in accordance with the recently introduced ‘Guide for the Design, Management and delivery of Pilots and Trials on the Highways Agency Network’4.
1.1 Evaluation Area
The evaluation area is shown in Figure 1.1. The evaluation of the impact of the traffic signal and ramp metering element of ITM was primarily focussed on the strategic and all-purpose networks in the vicinity of M1 Junction 33.
Figure 1.1 – ITM Evaluation Area
1.2 Evaluation Goals and Aims
The initial goals and aims for the evaluation of ITM around M1 Junction 33 were agreed by all stakeholders and were detailed in the evaluation plan5. Three main goals were identified as follows: ♦ evaluate the impact of the ramp metering system on the motorway traffic around M1 Junction 33; ♦ identify the impact of the ramp metering on local roads; and, ♦ evaluate the ITM management performance among the Highways Agency and local highway authorities.
4 Guide for the Design, Management and Delivery of Pilots and Trials on the Highways Agency Network’, PR241/06, November 2006. 5 ITM Evaluation Plan, [July 2007], Document no 5035805_02_03_04_005_Evaluation_Plan_Rev3.
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1.3 Evaluation Scenarios The initial evaluation plan allowed for a number of scenarios to be compared as was thought appropriate at the time. Owing to protracted planning issues surrounding the installation of MOVA at this junction, and other events, the evaluation plan was revised to provide two fundamental scenarios to test the effectiveness of this particular application of ITM. ♦ Scenario A – the original roundabout traffic signal times with ramp metering operational during September / October 2007; ♦ Scenario B – Revised traffic signal timings with the link to the ramp metering controller activated and operational during February / March 2008. In addition, during the initial review of the traffic signal timings, the queue override timings on the northbound and southbound motorway off-slip roads were not operating effectively. Following consultation between all the parties involved in the ITM Pilot, the northbound queue loops were repositioned. A full evaluation of the impact of this on the effectiveness of the junction operation has also not been possible as Automatic Number Plate Recognition (ANPR) equipment had not been installed to comprehensively monitor and quantify these changes. This was because ITM has no impact on the northbound exit slip road. However, observational comment is made on the impact of the loop relocation within this report.
Scenario B therefore incorporated more changes and improvements than just the technical ones brought about by installing a communications link between the two controllers and any benefits brought by this pilot include all these changes. Future ITM sites scheme managers should be aware that these changes, which may not be applicable to other sites, contribute to the benefits quoted in this report. For each scenario, it was anticipated that 20 days representative “before” and “after” data would be used for the evaluation. The data would be collected during weekdays only. The data collection period was extended to allow collection of sufficient data for differing traffic patterns. Collected data from days during which there were incidents or inclement weather conditions which could affect traffic flow would be excluded. Data were collected for 24 hour periods; however, the traffic conditions for ramp metering to switch on and provide data to the traffic signal controller are found predominantly during weekday peak periods.
It was initially anticipated that each of the scenarios would be independently operational for a period which would enable sufficient data to be collected and subsequently compared. A number of external factors outside the control of the ITM project, outlined below, were identified or were anticipated to preclude such an evaluation: ♦ long term road works between junctions 31 and 32 on the M1 and regular changes to traffic management layouts; ♦ long term road works on the A631, West Bawtry Road north of M1 Junction 33 influencing northbound traffic on Rotherway; ♦ early switch-on of ramp metering prior to the installation of evaluation monitoring equipment; ♦ developer funding for upgrade to MOVA deferred;
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♦ delays to the implementation of the ramp metering to traffic signals link; and, ♦ resurfacing works on the Sheffield Parkway. The additional plan to collect 20 representative days of data for each scenario, avoiding incident-affected days, holidays, and other abnormalities in flow patterns, also provided restrictions on the progress of the project given that for some periods it required over two months or more to obtain the required 20 data days. The likely effect of these external factors on the evaluation is discussed in Chapter 3, however, additional flexibility and alternative comparisons were incorporated within the evaluation plan to compensate for these changes.
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2. Evaluation Method
2.1 Periodicity and Data Selection
From a statistical perspective, traffic statistics are naturally periodic and this has been recognised in the analysis of the data collected. The general pattern that emerges when examining traffic data is that rush hour peaks occur at similar times each weekday, but superimposed on the daily range are much larger periodicities, both weekly (for example, Fridays are similar to each other) and annually (for example, August bank holiday traffic is similar from year to year). Traffic flows also have seasonal variations dictated by natural conditions such as the hours of daylight and the predominant weather conditions. These periodic patterns affect the flows, speeds and journey times observed.
The periodicity of traffic data is complex once the weekly and annual periodic patterns are considered, and in a relatively short study, it is not possible to collect sufficient data to adequately determine the effect that ITM has on traffic flows during the school holidays, or when other seasonal variations occurred. Therefore, traffic data from these days were removed from the sample.
In addition to the periodicity of traffic data, incidents on the road and adverse weather conditions cause aperiodic delay on the roads. These are not sufficiently frequent to allow the impact of ITM on the traffic flow to be analysed, therefore traffic data impacted by incidents and adverse weather was removed from the sample.
To try and ensure the information used for analysis for each scenario was a reflection of typical traffic conditions through the evaluation area, a process (see Figure 2.1) of data selection was adopted to remove data that were considered atypical.
This methodology removes the components of aperiodic delay caused by random events such as incidents and weather conditions, and also strong patterns in traffic data caused by regular annual events such as school holiday periods. With the time constraints on the evaluation, it was not possible to consider the impact of ITM in either aperiodically delayed traffic or seasonally variant traffic and thus it became necessary to obtain as much data as possible that did not deviate from typical conditions. The processing outlined produced traffic data from days that are directly comparable to each other.
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Obtain Data from Source
Is the data No complete?
Yes
Were there any incidents on this Yes day?
No
Was the weather No clear?
Yes
Were the local No schools open?
Yes
Were there any other seasonal Yes variations?
No
Data included for Data excluded evaluation from evaluation
Figure 2.1 – Data Validity Flow Diagram
2.2 Motorway (MIDAS) Data
Traffic counting information was recorded for the loop sites in the vicinity of M1 Junction 33 on both northbound and southbound carriageways. It was intended to record the same data from loop sites at M1 Junction 31; however, the loops were removed as part of the widening scheme taking place at the time.
Motorway Traffic Viewer (MTV) was used to plot profiles of the carriageway for traffic flows highlighting slow moving or stationary traffic on the main carriageway and assisting in the identification of incidents. MTV was also used to calculate the journey time of a vehicle through a selected section of motorway based on the measured speed at MIDAS loop sites in that section.
Reports for the southbound carriageway were requested from the TRADS6 system but the records were returned blank. Further investigation revealed the site was damaged in July 2006 during maintenance and was not repaired until the end of January 2008.
6 www.trads2.co.uk
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2.3 Journey Time Data
Journey time information from the Sheffield and Rotherham area was measured using ANPR cameras. Fourteen ANPR cameras were installed to create six journey time links (see Table 2.1) – one link required two cameras at either end to monitor two lanes in each location. The cameras were an integral part of the Sheffield CC journey time network and utilised their data analysis facilities. The resultant information was made available to the ITM evaluation team.
Table 2.1 – ANPR Link Details
Link ID Link Detail (See reference on Figure 2.2) Direction 250012 Sheffield Parkway to Rotherway (Both At M1 Junction 33) 3 → 5 250013 Rotherway to Sheffield Parkway (Both At M1 Junction 33) 6 → 4
250019 Sheffield Parkway M1 Junction 33 to Sheffield Parkway 4 → 2 Markets 250020 Sheffield Parkway Markets to Sheffield Parkway M1 Junction 1 → 3 33 250023 Sheffield Parkway (at M1 Junction 33) to Southbound On-Slip 3 → 7
250025 Rotherway (at M1 Junction 33) to Southbound On-Slip 6 → 7
Figure 2.2 details the locations in the context of the evaluation area as described in Section 1.1.
Figure 2.2 – ANPR Camera Locations
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Link 250020 was installed with the evaluation of the VMS in mind, and whilst the VMS element has been delayed, it has still been analysed to assess journey times heading towards the junction.
The journey times calculated for each of the identified links was used to plot frequency histograms of the times for vehicles to demonstrate the distribution of the journey times about the mean. The standard deviation of the journey times was also calculated.
2.3.1 Outlier Removal
ANPR camera systems measure journey times by recognising the same registration plates occurring at pairs of separate cameras. Due to the nature of motorways, it is extremely likely that the same registration plate occurring at two separate cameras on a motorway indicates a single continuous journey directly between the two cameras. The same cannot be said with the use of ANPR cameras on local roads; it is considerably more likely for extremely high journey times to be returned as a result of the following occurrences: ♦ vehicles may have deviated and changed their route before returning to the direct path through the link; ♦ vehicles may stop at some point within the link and exit the link at a much later time than for a continuous journey; ♦ a vehicle may be inherently slow moving (for example a wide load); and, ♦ the software may have returned an anomalous value. These occurrences return journey times that are much higher than the rest of the traffic data, and they do not reflect the traffic data that the study is interested in evaluating. The evaluation of ITM is interested in considering the direct journey times between pairs of ANPR cameras, and not in extremely high journey times that represent indirect journeys between pairs of ANPR cameras or journeys made by unusual vehicle types.
Within the traffic data these extremely high journey times will be visible as large outliers, and have the potential to skew the values of the sample mean and standard deviation away from the population mean and standard deviation of the direct journey times in which the study is interested. For this reason, outliers have been removed from the journey time data set before analysis was carried out.
More detailed discussion on outliers, the reasons for their removal and the statistical mathematics used is presented in Appendix A.
The mean journey times were compared for each scenario. The differences between the values indicate changes in traffic conditions as detailed in Table 2.2. In order to test the significance of the results, a Student’s t-test (see Appendix A) was performed based on the sample size, sample mean and the sample standard deviation; however, it should be noted that this test would not be able to distinguish why the difference occurs and that natural changes will always occur in traffic flows to some degree.
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Table 2.2 – Implications of Parameter Value Change for Journey Times Parameter Change Change Indicates Effect of Change Increase in Mean Travel time between Longer journey time nodes has increased Decrease in Mean Travel time between Shorter journey time nodes has decreased No Measurable Change in No variation in No measurable effect has Either Value travel time or profile been witnessed
2.4 Automatic Traffic Counter (ATC) Data
In addition to the above sources of data, SCC, and RMBC operate sites on the local network to monitor traffic volumes.
SCC and RMBC each collect data from two ATC sites in the evaluation area. Figure 2.3 shows the locations of the ATC sites.
The volume of traffic recorded at each ATC site was used to plot a profile of daily traffic volumes on the local roads in the vicinity of M1 Junction 33.
The ATC data was also used to identify abnormal occurrences through the evaluation area and also indicate all purpose network traffic flow trends through the assessment period.
Figure 2.3 – ATC Locations
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2.5 Ramp Metering and Traffic Controller Data
The system traffic log from the ramp metering controller and data from the traffic signal controller log were used to record the following data: ♦ the start time and end time of any ramp metering operational periods; ♦ the start and end time of the occupancy of each of the three ramp metering entry slip road queue detector loops; and, ♦ the start and end time of the occupancy of both the northbound and southbound exit slip queue override loops. The occupancy of the ramp metering queue loops results in changes to the ramp metering signal timings. This adjusts the balance between the requirement to meter traffic merging on to the motorway against the slip road queue length and its potential impact on the all-purpose circulatory traffic flows.
The occupancy of the off-slip queue results in changes to the junction traffic signal timings to ensure that traffic does not queue on to the main motorway carriageway to the detriment of the all-purpose circulatory traffic
The start and end time has been used to determine: ♦ the duration and the number of occurrences of ramp metering operation during its operational periods on a daily basis; ♦ the duration of the occupancy and the number of occurrences of the ramp metering slip road queue overrides; and, ♦ the duration of the occupancy and the number of occurrences of the off-slip road queue overrides.
2.6 Incident and Weather Data
Incident information covering Area 12 was filtered to show only incidents within or near the evaluation area. MTV was used to monitor the condition of traffic on the motorway carriageways.
Weather information was received in the form of a spreadsheet detailing the level of any rainfall and the effect on the flow of traffic the weather conditions had at particular times during the day. Any days where incidents or weather conditions affected traffic flows were removed from the relevant data scenario.
2.7 Incident Data
Incident information came directly from the local RCC for Area 12. This was used to remove days where incidents may have affected traffic flow through the junction.
In addition, MTV was also used to determine and confirm the presence of local incidents affecting the normal conditions on the motorway in the vicinity of M1 Junction 33.
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2.8 HANET data
The CCTV images available through HANET were also viewed on an occasional basis to confirm information provided through other sources.
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3. Relevant Events and Evaluation Timeline
This chapter summarises relevant events that have occurred during the evaluation and assessment of ITM from the commencement of the pilot project in October 2006.
3.1 Major and Long-term Events during ITM Evaluation
3.1.1 M1 Widening Scheme Junction 31 – Junction 32
The M1 was widened in both directions between junctions 31 and 32 during 2007. Work commenced on site in January 2007. The work was completed, and the new widened road opened on 21 December 2007.
The type of traffic management used during large schemes regulates the flow of traffic through road works such that downstream traffic flows are reduced. Once the scheme has been opened the traffic flow may return to previous levels or, in the case of widening schemes, may increase due to the increased capacity of the road.
During the course of the works, a 50mph speed limit was in force within the traffic management and as a result, significant queues built up on the approach to Junction 31 both northbound and southbound. Some northbound drivers also used the local road network to avoid motorway queues. A significant change to the traffic management on 12th November 2007 was also observed by the presence of larger than normal queues and increased flows in the local network.
The impact of these changes has been monitored though the motorway MIDAS and the all-purpose ATC data.
3.1.2 Sheffield Parkway Resurfacing Works
Since June 2007, the Sheffield Parkway has been undergoing a resurfacing scheme which reduced the speed limit on the road to 30mph on some occasions. Whilst the road works have remained in place for most of the data collection period, the traffic management pattern has changed which will lead to different constraints on the traffic flow on Sheffield Parkway. The road works may have also encouraged road users to find alternative routes.
The impact of these changes has been monitored through the all-purpose ATC and journey time data.
3.1.3 A631 Road Works
At the beginning of the evaluation, road works were present on the A631 North (Rotherway) and have been operational throughout the duration of the evaluation. Whilst these were not inside the evaluation area, this may have persuaded drivers to consider other routes before making their journey thus altering traffic flow. Traffic queues due to these works have influenced the journey times on the local road network as is discussed later in this report.
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The impact of these changes has been monitored through the all-purpose ATC data.
These works also caused power loss to ANPR cameras on Rotherway when a power cable was accidentally cut resulting in a loss of data. ATC information was also lost for a period during this time.
3.1.4 Ramp Metering Early Switch-On
The ramp metering at Junction 33 was switched on during September 2007. This was before the ANPR monitoring equipment had been fully installed and before the original baseline scenario could be evaluated. Thus, for all scenarios, ramp metering was active and controlling access to the motorway.
3.2 Evaluation Timeline
The timeline in Figure 3.1 documents the changes which may have had a bearing on the evaluation. A detailed chronology of events is provided in Table 3.1.
01/04/2007 - 01/06/2008 A631 Works
01/06/2007 - 31/12/2007 05/01/2008 - 06/05/2008 Parkway Resurfacing Parkway Works
01/06/2007 - 18/12/2007 M1 J31-J32 Works
15/07/2007 01/09/2007 13/11/2007 09/02/2008 ANPR Installed RM Operational NB Loop Modified ITM Operational
06/09/2007 - 24/10/2007 31/10/2007 - 02/02/2008 19/02/2008 - 30/03/2008 Scenario A ITM Calibration Scenario B
26/10/2007 - 30/10/2007 12/02/2008 - 16/02/2008 24/07/2007 - 31/08/2007 Half Term Half Term School Holidays 01/06/2007 30/05/2008
Figure 3.1 – ITM Project Timeline
The tracking of weather conditions, incidents and the validity of the information was completed separately. Only key events have been included in the table.
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Table 3.1 – Evaluation Timeline
Date Event Detail
31st July 2007 Ramp metering operation begins with original traffic signal timings.
3rd September “Before ITM” Scenario A begins. Data collection starts following 2007 school summer holidays. 30th October 2007 90 second traffic signal cycle time introduced.
3rd December 2007 60 second traffic signal cycle time introduced, revised plan timings operational.
13th December Northbound off-slip road loops cut. 2007 21st December M1 widening scheme between Junctions 31 and Junction 32 opened. 2007 January 2008 Road works on Sheffield Parkway. 30mph limit introduced. 6th February 2008 ITM timings introduced and validated. 8th February 2008 ITM switch-on completed and operational. 19th February 2008 “Scenario B” data collection begins following half term.
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4. Data Analysis - ITM Activation
4.1 Traffic Trends in Evaluation Area
The analysis of Scenario A data can be found in Appendix E, as can an analysis of traffic flow trends during the evaluation period. For the purposes of this report, the main findings have been summarised below: ♦ Traffic flow on the M1 had neither increased nor decreased during the evaluation period according to MIDAS flow data. ♦ The SCC ATC site detected an increase in traffic entering and leaving Sheffield City Centre over the course of the evaluation. ♦ An increase in traffic using the Mosborough Parkway was observed during November, which coincided with increased queuing on the M1 North at Junction 31. The volume reduced following the opening of the widening scheme. The increased flow on Mosborough Parkway is thought to be the result of drivers diverting via that route as an alternative to avoid motorway queues and rejoin the M1 northbound at Junction 33. ♦ Except for any natural fluctuations, no other ATC site reported an increase or decrease in volumes on the local road network. ♦ During the widening scheme between Junction 31 and Junction 32 the arrival pattern of traffic at Junction 33 had been changed and may have influenced driver behaviour patterns.
4.2 Journey Time through Junction 33
In order to compare the journey time of a vehicle travelling along the motorway through Junction 33 after the introduction of ITM (identified as Scenario B) with that of a journey conducted prior to its implementation (identified as Scenario A), virtual vehicle times calculated for Scenario B were compared to those presented for Scenario A. The results are discussed in this section.
The average journey time was measured over a 4km section of the M1; 2km upstream and downstream of Junction 33.
Traffic travelling northbound on the motorway is unaffected by ITM. Ramp metering has only been installed on the southbound carriageway. Furthermore, the traffic signal controller settings for the cycle time and the green time allocated to the release of traffic from the northbound exit slip road on to the roundabout are the same in both Scenario A and Scenario B. The comparison of journey times on the northbound carriageway therefore serves as a means of identifying any significant changes to flow levels entering the evaluation area.
Journey times are taken from the MTV Viewer which measures average speed at each MIDAS site and assumes that constant speed to the next downstream site. By this process a journey time is calculated over a range of loop sites. The measure is not as robust as the ANPR camera calculations but is the same method used for both scenarios.
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4.2.1 Northbound
Figure 4.1 – Comparison of Average Journey Time Northbound
The resulting profile for northbound average journey time suggests the morning and evening peak journey times have increased by approximately one minute between September 2007 and March 2008. The change is more prominent in the morning peak period shown by the larger difference between the profiles. However, the journey time did increase during the morning peak during Scenario A when compared to the rest of the day.
Analysis of MTV plots suggests the likely source of the increase in calculated journey time through the junction is the presence of queuing traffic on the exit slip road at Junction 33. Whilst this queuing will only affect vehicles in Lane 1, the virtual vehicle calculation is based on an average speed calculated across all three lanes thus making it sensitive to variations in any particular lane. Vehicles continuing their journey northbound on the M1 may not have experienced much delay at all. As the signal timings at the end of the exit slip road have not been altered under ITM, this increase in journey time is not attributed to ITM implementation.
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4.2.2 Southbound
Figure 4.2 – Comparison of Average Journey Time Southbound
The profile for southbound average journey time shows a change in average journey time during the evening peak period. The profiles above indicate that the maximum journey time observed has not increased during the peak period of Scenario B over that in Scenario A.
Figure 4.2 shows a significant variation in the journey times building up to the peak time (from 13:30), the mean journey time observed during Scenario B is lower than that of Scenario A indicating an improvement in journey time reliability on the motorway. The onset of delay is shorter during Scenario B, with the initial increase in journey time occurring approximately one hour after the same point during Scenario A. The mean journey time observed during Scenario A falls sharply before that of Scenario B at around 18:00, however, this deficit (as demonstrated by the area between the lines) is more than compensated by the benefit in the build up to peak time. This shift in the peak is the result of ITM extending the amount of time for queuing traffic to flush through the junction sustaining the journey time on the mainline.
The Scenario B profile suggests detrimental effects between 19:00 and 23:00, however, it is known that ramp metering is not operational during this time and so these oscillations cannot be attributed to ramp metering or ITM implementation. This prompted further investigation of MTV plots and revealed isolated incidents of loop faults on a particular day which were responsible for these anomalous peaks.
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Ramp metering is controlled by two algorithms, the primary one measures mainline congestion and sets a slip road release rate to maintain laminar flow on the mainline carriageway. However, the competing algorithm measures slip road queue formation and will increase the release rate to compensate. The latter therefore reduces the beneficial impact of the former. However, ITM controls the arrival rate of traffic at the slip road and reduces the queue giving back the incremental benefit to the mainline which Figure 4.2 suggests is happening at Junction 33.
4.3 Volume on the Local Road Network
Analysis of the ATC sites in the Sheffield area show the volume of traffic on the Sheffield Parkway to and from the city centre has continued to increase throughout the period of Scenario B (Appendix B, ATC 1 and 2). The increase since the beginning of the evaluation period is of the order of 4000 vehicles per day, between the hours of 7am and 7pm.
The data from the Mosborough Parkway ATC site (Appendix B, ATC 3 and 4) suggests that the volume of traffic using this road has increased marginally over the volumes experienced in September 2007. The data also suggests that volumes northbound increased significantly during November during the M1 widening works and that volume levels have since returned to normal following the opening of that motorway section.
The Sheffield Parkway ATC site, managed by RMBC, indicates (Appendix B, ATC 6) the volumes of traffic using Sheffield Parkway towards the city and towards M1 Junction 33 have remained constant. There appears to be a corresponding period in November of increased use, travelling towards Junction 33, which would appear to corroborate the hypothesis that northbound drivers were diverting from the M1 before Junction 31 and rejoining at Junction 33 to continue their journey.
The ATC site on Rotherway indicates an increase in the volume of traffic using this road travelling away from Junction 33. (Appendix B, ATC 7) This increase is of the order of 1000 vehicles per day since September 2007. The level of traffic is also much more stable since the beginning of the year with daily volumes constantly above 13000, whereby in the last quarter of 2007 the volume of traffic fluctuated greatly.
These increases in traffic flows are important as it can explain any changes in the journey time distributions in the evaluation area. An increase or change in volume would have a detrimental effect on the journey times of drivers given the increased competition for road space.
4.4 Journey Time Data
4.4.1 Preamble
The journey time data for each link during Scenario B were analysed and compared with the values calculated from the Scenario A data. The results can be found in Table 4.1.
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The change in the mean journey time was tested using the Student’s t-test7 with the null hypothesis ‘the mean journey times are the same’. (This is a standard statistical test which compares the sample mean, sample standard deviation and the sample size and is discussed further in Appendix A.) The results of the Student’s t-test can be used to reject the null hypothesis and conclude that the difference in the mean journey times is statistically significant.
A weighted average was then calculated as it takes into account the proportional relevance of each component rather than treating them all equally. The calculation used is detailed in Appendix A.
7http://www.itl.nist.gov/div898/handbook/eda/section3/eda353.htm
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Table 4.1 – Journey Time Analysis
Scenario A Scenario B Change in Change in Student’s t- Mean Standard test result at Mean Standard Mean Standard Link Period Deviation Deviation Deviation 95% confidence interval
24h - All Days Significant 250012 - Sheffield Parkway 101 22 107 26 5.3% +21% to Rotherway (North Across Peak* - All Days 110 29 113 18 3.3% -35% Significant Junction 33) Peak* - Fridays Only 104 13 107 15 3.0% +15% Significant 250013 - Rotherway to 24h - All Days 72 17 62 37 -15.8% +123% Significant Sheffield Parkway (South Peak* - All Days 84 18 76 30 -9.9% +69% Significant Across Junction 33) Peak* - Fridays Only 81 11 73 28 -10.3% +152% Significant 250020 - Sheffield Parkway 24h - All Days 269 55 252 56 -6.5% +3% Significant Markets to Sheffield Peak* - All Days Significant Parkway (West to Junction 307 83 285 96 -7.6% +15% 33) Peak* - Fridays Only 295 57 252 28 -17.0% -52% Significant 250023 - Sheffield Parkway 24h - All Days 85 43 73 29 -16.7% -34% Significant to M1 Junction 33 Peak* - All Days 107 58 83 32 -28.8% -45% Significant Southbound Slip Road Peak* - Fridays Only 93 27 79 31 -16.8% +16% Significant 250025 - Rotherway to M1 24h - All Days 46 12 37 31 -23.2% +166% Significant Junction 33 Southbound Peak* - All Days 54 15 46 28 -19.1% +92% Significant Slip Road Peak* - Fridays Only 54 11 42 24 -27.1% +114% Significant * Evening Peak
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4.4.2 Journey Time Results Discussion
Link 250012- Sheffield Parkway to Rotherway (North across Junction 33)
The mean journey time for this link has increased marginally across the entire data set. The results of the Student’s t-test suggests that the change in mean journey time is significant and in particular that the mean journey time is likely to have increased across this link.
The change in the standard deviation indicates the reliability of journey times has decreased slightly during peak periods on Fridays, and across the entire period of analysis. The peak period between Monday and Thursday is an exception to this where a decrease in the standard deviation indicates reliability has increased.
Analysis of the distributions uncovers the underlying reasons for the increase in the standard deviation calculations. Across all periods the distribution has increased in width as the change in standard deviation indicates. However, this increase is due to a larger number of lower data points observed in Scenario B than in Scenario A. There is no significant increase in the maximum journey time observed (Appendix C, C1 and C2). This means more journeys are taking less time than the mean time without any increase in the number of drivers experiencing a longer journey time.
Road works on West Bawtry Road are known to have caused a build up of traffic at the roundabout to which the northbound Rotherway joins. It is reasonable to expect that this build up spilled on to Rotherway reducing the speed of vehicles on approach to the roundabout and may have caused free flow conditions to deteriorate. The position of the end node is close to the roundabout at the north end of the Rotherway where this effect will be more pronounced and cause a greater reduction in speed. ATC data indicates a reduction in average speed during peak times of 4-5mph on this road since September 2007. This has in turn increased the time taken to exit the link causing a disproportionate increase in the journey time measured. Due to the location of the end node, any benefits brought by improvements at Junction 33 are quickly absorbed by any negative changes to traffic flows going north on the Rotherway.
ATC data does indicate an increase in traffic volume going North on Rotherway over the course of the evaluation and the effect of a natural increase in traffic volume cannot be ruled out as a contributing factor. It is not possible to determine whether the introduction of ITM is the cause of the increase in mean journey times.
The changes in the standard deviation reported is the result of values skewing the calculation rather than a change in the distribution profile.
Link ID 250013 - Rotherway to Sheffield Parkway (South across Junction 33)
This is an important link calculation as one of the key objectives of the pilot project was to assess the impact of ITM on the local traffic traversing the roundabout.
The mean journey time for this link has decreased across all periods. However, the standard deviation has increased by a significant amount across all periods. This increase in the standard deviation would indicate that more journeys are markedly
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longer or shorter than the mean journey time and the journey time in the link has become more unreliable. The distributions for Scenario B, across all periods, show a significant change in that the distributions have become much wider with lower peaks. This supports the change in the standard deviations reported.
As the length of green time on the Rotherway approach was altered during the calibration, the pattern of arrival across the gyratory will have also changed resulting in longer or shorter duration stops at each stop line and thus affecting the overall time to traverse the link. This change is the reason for the large differences to the distributions across all periods and has given the impression of a decrease in reliability when the signal conditions for Scenario B are not the same as those for Scenario A and a direct comparison between the standard deviations is not reasonable.
The ATC data indicates there has been no increase or decrease in the volume of traffic using Rotherway southbound.
The results of the Student’s t-test indicate that the change in the mean journey time is statistically significant, and it is likely that there has been a reduction in the mean journey time over the course of the study.
Link ID 250020- Sheffield Parkway Markets to Sheffield Parkway (Towards M1 Junction 33)
This link will not be affected by the operation of ITM, but has been included to assess the journeys of vehicles approaching the evaluation area and the effects of road works.
The mean journey time for this link has decreased across all periods. The spread of journey times has decreased significantly for Friday peak periods but for all other periods it has increased.
The effect of resurfacing works on Sheffield Parkway cannot be ignored given the large change in the spread of journey times calculated. This reduction in journey times is most likely attributed to the works as it is unlikely this dramatic change would be solely the result of ITM implementation further upstream. It is not possible to separately identify the effect of ITM and these works from the data collected. The distributions across all periods (Appendix C, C13 and C14) are near identical which explains the small difference in their standard deviations. The reduction in the standard deviation during Friday peak periods is a result of a reduction in long duration journey times, which were observed in Scenario A. These long journey times, which may have been a result of the road works, have increased the difference by skewing the Scenario A value.
The Student’s t-test indicates that the change in the mean journey times is statistically significant.
The peak mean journey time across the link is lower and journey times are much less variable than the overall (24hrs) mean journey time in Scenario B. This suggests that some of the traffic is much slower outside peak hours than inside them and may be due to the relative levels of HGVs using the link in peak and non-peak times. The reductions in journey times also suggest that drivers will be approaching Junction 33
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earlier than in Scenario A requiring the ITM to cope with an increase in peak demand.
Link ID 250023 - Sheffield Parkway to M1 Southbound On-Slip
The mean journey time for this link has decreased across all periods with the greatest decrease found in the evening peak period Monday to Thursday. The spread of journey times has also dropped considerably for the same period. However, when looking at Friday peak periods only the range of journey times has increased. The Student’s t-test indicates that the change in the mean journey time between the scenarios is significant.
The traffic distributions point to a reduction in the number of long journey times between the scenarios as the reason for the reduction in the standard deviation. Where the standard deviation has increased, during Friday peak periods, the width of the distribution has increased due to a relative increase in lower journey times rather than an increase in the number of long duration journeys. This would account for the small increase in the standard deviation reported and is not thought to be symptomatic of a reduction in journey time reliability.
The Sheffield Parkway approach is the only signal phase directly controlled by ITM and is dependent upon the queuing information received from the RM controller. ITM has had a positive impact on traffic using this link with reduced journey times. The spread of journey times has reduced with the exception of those conducted on Friday afternoons where ITM is actively attempting to manage the peak queues on the roundabout prior to release on to the slip road. It may be this queue management effect that is increasing the standard deviation on Friday peak periods.
The impact of introducing ITM has improved queuing. There is more competition for road space on this approach given that analysis of link 250020 suggests that traffic is approaching Junction 33 from Sheffield Parkway Markets faster due to the reduction in the mean journey time.
Link ID 250025 - Rotherway to M1 Southbound On-slip
The mean journey time for this link has decreased across all periods. However, the standard deviation has increased dramatically for each period indicating a reduction in the reliability of journey times through this link. The journey time distributions for Scenario B all show large changes which are attributed to the large number of journeys observed away from the mean, extending the width of the distributions. The distribution for Friday peak periods in Scenario B (Appendix C, C30) shows no defined peak at all.
Link 250025 shares a common factor with that of link 250013 where the green time at Rotherway approach to the roundabout has been altered resulting in a change to the arrival patterns through the gyratory. This is the reason why the distribution for all periods has changed so dramatically in line with the same results found in link 250013. Since the ATC site shows the volume of traffic on Rotherway South has remained constant this change cannot be attributed to a change in volumes. The signals on the Rotherway approach are not yet curtailed by ITM and so ITM is not the cause of this change either.
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The results of the Student’s t-test indicate that the changes in the mean journey time are statistically significant.
4.4.3 Impact of ITM on the Local Road Network
Table 4.2 – Weighted Averages Difference in Difference in Weighted Weighted Link Mean (All Means (PM Periods) Peak) 250012 - Sheffield Parkway to Rotherway 4.8% 3.8% (North Across Junction 33)
250013 - Rotherway to Sheffield Parkway (South -14.4% -9.8% Across Junction 33)
250020 - Parkway Markets to Sheffield Parkway (East -7.2% -8.6% from Junction 33)
250023 - Sheffield Parkway to M1 Junction 33 -19.6% -26.2% Southbound Slip Road
250025 - Rotherway to M1 Junction 33 Southbound -22.6% -20.1% Slip Road
Across All Links -8.7% -9.8%
The data collected from the ANPR journey time system indicates that the ITM project has resulted in a reduction of journey times on the local road network in the evaluation area. Typically, the mean journey time on the links analysed, tabulated in Table 4.1, has been reduced by between 7% and 29% depending upon the period of evaluation, and in all cases this reduction is statistically significant. Table 4.2 shows the weighted average for each link across all periods and evening peak periods (when ramp metering operates). The weighted average difference across all links, during all periods, gives an overall reduction of journey times by an average of 8.7%. This reduction is further enhanced during ITM operation with an overall reduction in journey times of 9.8%
The reductions across all periods are likely to be the result of the improved conditions at the junction and the improvements made to the traffic signal controller timings as ITM and RM are unlikely to be operational outside the evening peak period. The benefits brought by these alterations are present throughout all periods and so the reduction quoted for peak periods (9.8%) is a combination of benefits brought by ITM and the improvements to the junction. It has not been possible to extract the benefit
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of ITM only but it may be concluded that a net benefit exists in the local road network during the periods when ramp metering and ITM are active.
The only link directly controlled by ITM, and most affected by its implementation, is link 250023 (Sheffield Parkway to M1 Junction 33 Slip Road). The weighted benefit during peak times shows a very significant reduction in journey times, however, relative to the benefits observed outside periods of ITM operation much of this reduction can be attributed to the controller improvements. These further improvements may be a result of reduced queuing on the approach to the junction or better queue management on the entry to the slip road - an improvement brought by ITM. The RMBC ATC data suggests that as the volume of traffic approaching Junction 33 on the Sheffield Parkway has remained consistent during the evaluation period, the reduction is attributed to better management of the capacity within the link rather than a reduction in volumes.
Traffic crossing the junction travelling northbound from the Sheffield Parkway to Rotherway was the only link to report an increase in journey time. Road works on West Bawtry Road may have had an impact on the time at which vehicles reached the end of the journey time node due to their reduced speed. This disproportionately extends the journey time. A comparison with the link from Sheffield Parkway to Junction 33 on-slip which is a similar length journey supports the hypothesis that detrimental factors must be limited to the Rotherway, since both links cover the same route for part of the journey time calculation. The reported increase in volume, as shown by the ATC data, may have cancelled out any benefits that ITM did bring due to decreased speed approaching the downstream Rotherway roundabout.
The potential impacts of resurfacing works on Sheffield Parkway should not be ignored as the disruption caused by such work will inevitably affect journey times and the distribution of those journey times. The changes to the dynamics of the road network by the widening works on the M1 at Junction 31 to Junction 32 have also been observed from the ATC sites. Continuing road works on the Sheffield Parkway will also have affected the journey times collected for the Scenario B data.
The distribution of the journey times have significantly changed in some cases which may be a direct result of the changes within the evaluation area. Many of these changes are not explicitly a result of a change in journey time reliability. They represent a change in the conditions when the observations were made, thus leading to a variation in the journey times detected affecting the calculation of standard deviation. It is not clear that the implementation of ITM is the only factor which has contributed to the more reliable journey times found on some links in the study.
The resulting Student’s t-test on the data samples indicates the population mean has changed and the resulting differences between the two scenarios are significant for all the links analysed. The anticipated benefits of ITM at its concept stage were thought to be in the region of 0.5% to 1% based on micro simulation modelling. Given the level of disruption within the evaluation area, and the likelihood that natural traffic variations would have occurred regardless of ITM activation it is not possible to attribute benefit directly to implementation of the data link between the ramp metering controller and the traffic signal controller in isolation. It is a combination of events that has resulted in the benefit to the network as a whole, principally the complete revision to the operation of the signals at this roundabout necessary to introduce the
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interface to the ramp metering controller. This has resulted in an all round improvement to the operation of the roundabout.
The traffic signals operate under the control of Cableless Linked Facility (CLF) plans and these fixed time plans have been set up to optimise the flows at the roundabout. The data from the ramp metering controller is intended to make small incremental changes to those optimised plans and therefore, with this particular control strategy, it is very difficult to identify the direct impact of those changes. However, it is not unreasonable to conclude that ITM has been successful when viewed as a complete review of the operation of the junction. Had the operational strategy of the traffic signal controller been a dynamic one, such as MOVA, when the traffic arrival rate at the metered stop line can vary more, the influence of the linking to ramp metering would have been more pronounced. By the nature of its method of operation, the fixed times configured in the CLF plans do not allow sufficient variability for the ITM control loop to influence the behaviour of the signals in the same way that would be the case if a more variable traffic control strategy were to be in place. It is therefore a recommendation of this report that ITM should be trialled on a similar network operating a dynamic traffic signal control strategy.
4.5 Impact of ITM on the Motorway Southbound Carriageway
4.5.1 Calibration Changes
At the outset of the pilot project, RMBC had expressed their concerns that local traffic between Rotherham and Sheffield would suffer additional congestion caused by the introduction of ramp metering on the southbound slip road. The ramp metering system was therefore conservatively calibrated to ensure that queues did not extend beyond the slip road and congest the roundabout. Of the thirty ramp metering sites installed and calibrated in 2007, this particular site alone was biased to prevent excessive queuing because of the local concerns. The initial release rate at this site was conservatively set to allow 980 vehicles per hour to be metered on to the main carriageway. A more restrictive setting allowing fewer vehicles on to the motorway would have further reduced the journey times for traffic on the mainline. The initial calibration settings produced a benefit of 9.1% savings in average journey times compared with the situation before ramp metering was installed.
Following the introduction of ITM improvements within the network, the ramp metering site was recalibrated to remove the conservative settings and allow the other changes at the junction and the linking to contribute to the management of flows to the slip road. With ITM operating, the revised timings restricted the release rate to an average of 780 vehicles per hour without an adverse effect on the slip road queue formation.
Logically, the reduced rate of joining traffic results in lower disruption to mainline flow from merging traffic. Local observations have confirmed an improvement to the general operation of the ramp metering site.
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4.5.2 Assessment of Calibration Changes
Following the activation of ITM, the impact of the ramp metering system on the main motorway carriageway was reappraised to ascertain if the addition of ITM had reduced or increased the benefits previously measured. The data collected was extensively checked and filtered to ensure that as far as reasonably possible, the evaluation was based upon a true and fair comparison of traffic conditions in the period before ramp metering and after ITM. This included: ♦ identifying and excluding days with incidents using a visual inspection of Motorway Traffic Viewer (MTV) plots and Regional Control Centre (RCC) incident data logs; ♦ identifying and excluding untypical days such as bank holidays and school holidays; ♦ classifying and excluding days according to rainfall data obtained from weather monitoring sites in each area; and, ♦ identifying the typical operational periods for each site from the ramp metering system log files. Data was used from a period before the installation of the ramp metering system and following the successful calibration and implementation of ITM when other changes were made to the ramp metering calibration to accommodate ITM.
The length of M1 over which journey times have been assessed is 4.8km. It has been observed that the traffic flows away from Sheffield are high in the weekday evening peak, leading to congestion at Junction 33 southbound. It was therefore decided to focus on the analysis of ITM performance in the weekday evening peak periods
The study period of ramp metering operating with ITM was from 8th February to 16th May 2008; of which 23 days were used for analysis. The 23 days of data were then averaged to produce an average journey time and traffic flow over the evaluation period using the same method of calculation as in the previous analysis. Table 4.3 shows the results from the evaluation.
Table 4.3 – Ramp Metering Evaluation Results
No System RM Only RM and ITM
Average Journey 294 267 250 Time Change in Journey N/A -9.1% -14.7% Time
The data analysed following the introduction of ITM demonstrates an improvement in the benefit on the mainline carriageway with a total average reduction in journey time saving of 14.7% compared with the case before ramp metering was introduced. Further analysis also revealed the mainline carriageway flow has increased by an average of 140vph during this time.
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4.6 Improvements to the Mainline Flow
Changes to the ramp metering calibration settings and the introduction of ITM has had a positive benefit on the average journey times for southbound traffic on the motorway main carriageway. However, it would be incorrect to attribute the measured improvement on the motorway solely to the ITM implementation and the recalibration of the ramp metering system. Other factors, such as the impact of the motorway widening, are likely to have had some impact on the improvement. It has not been possible to definitively quantify benefits solely from the ITM improvements.
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4.7 Cost Benefit Analysis
4.7.1 Assumptions
ITM is not a technology in its own right but is the integration of existing technologies in a more effective manner. In the case of the M1 Pilot Project this represents the integration of ramp metering with traffic signal control on the adjacent junction roundabout.
Ramp metering has been developed as a technology to delay the onset of flow breakdown on the main carriageway of a motorway by controlling the release of traffic on to the motorway when the existing flow is approaching the onset of flow breakdown. This technique has been carefully evaluated at a number of sites on the network and improves the main carriageway journey time by an average of 10%.
Traffic signals are installed on approximately 180 motorway junction roundabouts to better manage traffic demand and these have usually been installed with the principal aims of preventing gridlock and maintain the circulating traffic flow and to allow traffic to leave the motorway without queuing back along the off-slip road and on to the main carriageway. Traffic signals operate a number of strategies including CLF (as at M1 Junction 33) and MOVA. Costs for such signals vary depending on complexity, control strategy and junction geometry but are conservatively estimated to cost between £250,000 and £500,000 for a control system to current standards. At more complex junctions this cost may be exceeded. These costs are justified by junction demand management and therefore excluded from any cost benefit analysis of ITM.
4.7.2 ITM Operation
ITM operates by sending queue status messages to the local traffic signal controller which are connected to the existing detector input interface. No special adaptation of the controller is required. The way these bits are used to influence the operation of the signals is determined by the special conditioning logic programmed into the controller as described in Appendix D. There are no special modifications necessary to the functionality of the controller, its hardware or its software.
It is important to recognise that every junction is different with differing geometries, traffic composition and demands and therefore there is no standard method of implementing ITM. Each site requires the analysis of existing controller operational timings and the introduction of reductions in certain green times on the receipt of the queue status messages from the ramp metering controller. Thus, the success of ITM is dependent on the experience of the traffic signal engineer to adjust green splits and the overall cycle times to optimise the operation of the junction. This is the most costly element of introducing ITM.
ITM influences the operation of the controller locally. In the case of the M1 Pilot Project an outstation transmission unit was added with a broadband link to the traffic signal control centre in Sheffield. This not only allowed the local authority to monitor the operation of the junction in real time which had not been previously available but provided additional information to the UTC centre about the state of congestion on the motorway. It is already planned to use this data to trigger the display of traffic
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information on a VMS advising the alternative route to M1 Junction 31 but it could in future be used to influence other traffic control plans in other parts of the network. The benefits of such information are excluded from this analysis.
4.7.3 ITM Installation Costs
The principal equipment supply cost of ITM is the physical link between the traffic signal controller and the ramp metering systems described above. On the M1 pilot system, queue status messages are transmitted to the traffic signal controller to give a measure of the percentage occupancy of the slip road. This was achieved with an industry standard single direction radio link at a cost of £2,500 for the supply, installation and commissioning of the unit. A conservative estimate of the additional installation costs for minor civil works adds approximately £7,500 to the supply cost. Alternatively, this link could have been provided by direct buried cable but in this instance, it was not cost effective to do so. The latter would have significantly added to the traffic management costs which were minimal for the radio link installation.
The revenue costs associated with ITM are the minimal power supply costs for the link equipment and the broadband link. These are considered negligible.
4.7.4 ITM Technology Costs
The cost to design and validate the revised traffic signal timings at Junction 33 is the major cost of introducing ITM. The traffic signal design costs, including site testing and validation were approximately £55,000 over the life of the project. It is the design skills and experience of the traffic signal engineer which ensures the success of the ITM strategy and therefore must be included in any cost benefit analysis. The principal costs of ITM are summarised in Table 4.4.
Table 4.4 – ITM Costs
Item Capital cost
Supply and installation of ITM specific £10,000 equipment
Design and validation of the traffic controller £55,000 operation.
Total £65,000
4.7.5 Supporting Costs
ITM should not be viewed as the application of technology alone. Whilst integrating traffic signal control and ramp metering systems with a simple method of linking remains at the heart of the pilot project, one of the fundamental costs of implementing a successful ITM scheme is the emphasis placed on local liaison both with contractors and the local authorities themselves. There is naturally a cost associated with this.
In the case of this pilot project, Rotherham MBC is the highway authority for the M1 Junction 33 roundabout and Sheffield City Council operate the junction on its behalf.
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The Highways Agency maintains the signals through its maintenance agent, CarillionWSP who in turn sub-contract the specialist signal maintenance to Peek.
A Steering Group was established for the ITM project as a forum for the exchange of information and equitable resolution of issues arising. This forum included the Highways Agency, Sheffield City Council, Rotherham Metropolitan Borough Council and the Highways Agency’s maintenance contractor, CarillionWSP. The Steering Group met monthly and was one of the key drivers for the project. The costs of maintaining monthly meetings and recording the deliberations of such a group and responding to actions arising will vary from project to project but should be considered as a real project cost. The Steering Group met fifteen times during the course of this ITM project with all parties bearing their own costs. A collective cost is not available.
The Junction 33 ITM scheme was also carefully evaluated using extensive data from many sources as described elsewhere in this report. Collecting and analysing this data and the subsequent preparation of this report also incurred costs. As this was a formal pilot project considerable emphasis and cost was incurred. Evaluation costs were between £150,000 and £200,000 and involved work by local authorities, the Highways Agency and its agents and consultants.
The costs of supporting a project of this nature should be recognised but have been omitted from subsequent cost-benefit analysis as they will vary from project to project and, in the case of a formal evaluation may not apply at all.
4.8 Benefits
4.8.1 Local Authority Benefit
Table 4.5 provides an indication of the potential economic benefits of the implementation of ITM from the local authority perspective. In this case, the costs of modifying the traffic signal controller and providing the link to the ramp metering equipment contributes most to the improvements in the local road network.
Average evening peak turning flows at the roundabout junction have been utilised with the observed journey time changes to develop evening peak changes in overall costs. Where changes are observed as detrimental, the greater of either the ‘24hr - All days’ or the ‘Evening Peak - All days’ change in mean journey time has been used so as to err on the pessimistic side. Where changes are observed as beneficial the smaller values have been adopted. Thus, the benefit value claimed for the scheme is based on the minimum value of benefit drawn from the statistical evidence. No benefits from the operation of ramp metering are included in this part of the assessment.
This results in an overall benefit of approximately £104 per PM peak hour. It should also be recognised that traffic signal improvements benefit the junction throughout the day and not just when ramp metering is operating.
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Table 4.5 – Indicative Benefits
Ave PM Total Vehicle Peak Ave JT Ave JT Vehicle Change hour flow (sec,) (hours) Hours in JT change Parkway to Rotherway (North Across Junction 800 110 0.030 24.4 3.8% 0.93 33)
Rotherway to Parkway (South Across Junction 650 72 0.020 13.0 -9.8% -1.27 33)
Parkway to M1 Junction 33 Southbound Slip 1100 85 0.024 25.9 -26.2% -5.09 Road
Rotherway to M1 Junction 33 Southbound 400 46 0.013 5.1 -20.1% -1.02 Slip Road Total change vehicle hours -8.17 Benefits @ £12.738 per vehicle hour £103.97
Assuming the estimated ITM installation costs of £65,000 (Table 4.5) and estimated annual maintenance costs of £1,500 per year over a lifetime of five years gives a net present cost of approximately £70,000 giving an approximate pay back period of just under five years. The benefit to cost ratio over the first five years is 1.43. However, this takes no account of any benefit to the motorway discussed in the next section.
4.8.2 Benefit to the Highways Agency
Journey time improvements along the southbound carriageway of the motorway provide the cost benefit for ITM. The improvements to ramp metering and the recalibration exercise have contributed to an improvement in the journey time saving from 9.1% to 14.7% compared with the time before ramp metering was introduced. It has already been stated that this benefit cannot be attributed exclusively to the introduction of ITM but the latter certainly contributes to the overall improvement.
The average southbound traffic flow through Junction 33 between 16:30 and 19:00 during weekdays is approximately 3400 vehicles per hour. The average delay per vehicle reduced by 27 seconds in the initial assessment of ramp metering. Following recalibration as part of the ITM improvements at the junction the delay per vehicle was 43 seconds. The difference represents a total reduction of vehicle delay of 15 vehicle hours per hour in the evening peak period.
Whilst it is reasonable to attribute some of this benefit to the ITM project there is no irrefutable evidence that allows one to draw the conclusion that all the benefit may be attributed to ITM. For this reason, converting an obvious improvement into monetary terms as a direct benefit of ITM would be potentially misleading.
8 http://www.webtag.org.uk/webdocuments/3_Expert/5_Economy_Objective/3.5.6.htm#012 Paragraph 1.2.30 adjusted to 2008
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However, if only a part of this improvement were attributed directly to ITM, the pay back period for the ITM investment is clearly much shorter.
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5. Conclusions
5.1 Introduction
The aim of the ITM Pilot Project, as defined at the project inception, was “the integrated application of existing traffic management techniques on national strategic routes and the associated network corridor of adjacent roads and interchanges to manage access to, and from, the strategic route network by optimising vehicle delay in the combined strategic and local road network”.9 The project’s success must therefore be measured against the prime objective of reducing congestion in the combined road network. This means that ITM must be viewed as an approach to improving the combined network through using technology as a means to an end.
5.2 Journey Time Savings
The weighted journey time saving for traffic using the local road network is 8.7% across all periods, with an increase in the saving during peak times to 9.8%. In addition, we have reassessed the journey time savings to traffic on the motorway southbound carriageway. Following the introduction of ramp metering at this site, the average journey time saving was 9.1%. Using the same sources and methodology, the measured benefit after ITM was introduced increased this to 14.7%.
Reliability of journey times in the local network before and after the introduction of ITM is approximately constant.
The linking of the two systems on Junction 33 has had a positive effect as indicated by the reduction of journey times on the local road network and the improvements to the mainline southbound carriageway. However, the levels of reduction are higher than originally anticipated and as a result these reductions cannot only be the positive result of linking the two systems, but must be additionally attributed to the following changes that have also occurred as a direct result of the project’s activity at Junction 33: ♦ introduction and recalibration of ramp metering on the southbound slip road; ♦ revalidation of the traffic signal controller timings; and, ♦ improved levels of maintenance management and actions to correct detector operation of the original signals. From the earlier micro simulation modelling, it was anticipated that linking roundabout traffic signals and the associated ramp metering system would only produce benefits of 0.5% to 1% attributable to the linking changes alone. This expected benefit has been difficult to isolate from the combined effect of changes to traffic signal operation and the ramp metering system necessary to accommodate that linking. ITM must therefore be seen as a holistic approach to better managing the network surrounding motorway junctions and its results judged accordingly.
9 ITM Final [Feasibility] Report, Motorway Access Management Project, 5032714, Document 001_0072_T_554.doc, April 2006
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Natural variations within traffic flows also influence the reported benefits and should not be discounted. The level of external disruption within the evaluation area has also had an impact on the significance of the results achieved. The level of improvements as indicated by the reductions in journey times should be conservatively interpreted given the levels of statistical noise that have been experienced.
There have been many factors which have influenced the evolution of this project and which have a bearing on the results achieved particularly the impact of the motorway widening at Junction 31 to Junction 32
However, it is clear that the pilot project has delivered a positive benefit and has improved the operation of the motorway and the local road network.
5.3 Stakeholder Involvement “As operator of the Junction 33 signals on behalf of Rotherham BC and the Highways Critical to a project of this nature is the Agency, Sheffield CC was involved with the cooperative working and decision making work to modify the operation of the junction. necessary between all parties. Throughout the However, we were also concerned because project, both SCC and RMBC have been an a substantial proportion of the traffic integral part of the Steering Group and have passing through it has an origin or contributed towards the success of the project. destination in the city. We feel that the ITM project provides a model for engagement The views of the local government bodies are between the Highways Agency and local appended to these conclusions. highway authorities to consider management of traffic at the interface between the Agency and local networks. It The Steering Group had a major influence on was very useful to be able to input local the success of the project. In particular, knowledge and priorities at the earliest stages of the project, and to maintain ♦ operational traffic management strategies contact throughout its development. The were agreed collectively; project has improved liaison between all ♦ work share was better coordinated the organisations involved, this bodes well amongst partners and was thus more for the co-operation that will be required to efficient; maintain efficient operation during its on- going life. The long term involvement of the ♦ maintenance procedures were optimised Council has allowed us to identify a number and improved; and, of additional pieces of work augmenting the project which have increased the efficiency knowledge exchange from different ♦ of our monitoring of the junction and the political and operational perspectives local roads in the area. We feel these are a enhanced the original concept of ITM direct benefit which would not otherwise operation. have been secured.” Peter Bull 5.4 Technology Sheffield City Council The positive technical aspects of the project are that: ♦ reductions in journey times have been identified on both the local and motorway networks; ♦ queue management on the slip road where ramp metering has been installed can be positively managed with the adjacent traffic signals;
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♦ the additional effort required to integrate the technologies of ramp metering and traffic signal control is inexpensive; and, ♦ a general improvement to the operation of the traffic signals outside the operational hours of ITM was achieved. In addition, the original local authority concerns about the operation of ramp metering and, in particular, the potential for queues to extend on to the local road network have not been realised.
“Rotherham Metropolitan Borough Council are Highway Authority for the A630 approaches to Junction 33 of the M1 Motorway and also for the circulatory carriageway of the roundabout. The Council was approached by the Highways Agency and invited to participate in the ITM Pilot Project, along with Sheffield City Council; the three highway authorities to be equal partners in the project.
The formation of the Steering Group enabled an extensive amount of local knowledge from the three highway authorities to be fed into the study, and the enthusiasm and commitment by all the partners ensured optimal progression of the project. All partners have become increasingly aware of the priorities and concerns of the others, particularly in the appreciation of the political dimension at a local level. The project has contributed to developing improved lines of communication between the highway authorities. Correspondingly, working relationships have benefited resulting in more effective delivery of the ITM project. It is likely that through these improved relationships, which would not have developed otherwise, future schemes involving the Highways Agency and local highway authorities may be better delivered.”
Ian Ashmore Rotherham Metropolitan Borough Council
5.5 Recommendation ITM was installed at the pilot site by influencing a traffic signal controller operating CLF plan timings. Such plans are based on historical data and their efficiency will deteriorate unless the data upon which they are based is reviewed from time to time. The project highlighted the lack of coordination between the operation and maintenance responsibilities at this junction. It is recommended that the Steering Group is reconstituted to address these issues under the chairmanship of the HA Area 12 Route Performance Manager. Dynamic operational strategies such as MOVA vary flows from traffic signal cycle to cycle and thus the arrival rate at a metered slip road will be variable. The success of the ITM concept cannot be fully recognised until the technique is proven at traffic signal sites which are operating such a dynamic control strategy. It is a regret that the planned installation of MOVA at the pilot site during the project was not possible because of evolving planning issues. It is recommended that the next phase in ITM development should be to take the lessons learnt at the pilot site and apply them to a junction site where the local signals are operating MOVA.
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Glossary
ITM Integrated Traffic Management
ATC Automatic Traffic Counter
MTV Motorway Traffic Viewer
ANPR Automatic Number Plate Recognition
VMS Variable Message Sign
SCC Sheffield City Council
RMBC Rotherham Metropolitan Borough Council
MIDAS Motorway Incident Detection and Automatic Signalling
CCTV Closed Circuit Television
SPSS Statistical Package for the Social Sciences
CLF Cableless Linking Facility
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Appendix A – Statistical Tools
In order to evaluate ITM, a number of statistical tools were used to analyse the data and provide quantitative calculations. This appendix will explain the tools used and the significance of the outputs from them.
Mean and Weighted Average
The simplest statistical value of any set of measurable data is the mean, (more commonly known as the average). It is calculated as the sum of all data values, divided by the number of samples. The equation for the arithmetic mean is below:
1 n x = ⋅∑ xi (1) n i=1
The mean is a good indicator of changes between two sets of data, i.e. a lower mean indicates a decrease in the sample values as a whole. However, it is worth noting that the mean is particularly sensitive to the presence of outliers, and is not always representative of a ‘typical’ sample. For this reason, where systematic outliers are likely to be present in data, steps must be taken to screen the data for outliers to remove any potential oddities that will adversely affect the mean.
The weighted average takes into account the relative size of the samples used to calculate the mean, so it is more accurately related to the samples rather than treating them all as equal components. It is calculated as the sum of each sample mean multiplied by its sample size divided by the sum of all the samples:
()n x + n x + + n x y = 1 1 2 2 K i i (2) n1 + n2 +K+ ni
Standard Deviation
The standard deviation is the root mean squared deviation of values from their arithmetic mean. It is calculated by taking the square root of the average of the squared difference between each value minus the mean, as shown in the equation below:
n 1 2 σ = ⋅ ∑()xi − x (3) n i=1
The standard deviation is a very good indicator of the width of the data distribution. A large standard deviation indicates a wide ranging set of values, whereas a low standard deviation indicates a set of values closely associated with the mean of the data. As with the mean, an outlier with a large or very small value will also increase the standard deviation.
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Histograms
Histograms are a graphical representation of the frequency distribution of data, it is a graphical version of a table that shows the number of values, or frequency of values, that fit into a certain category (or ‘bin’). Histograms differ from conventional bar charts in that the area of each bar represents the value rather than just its height. (This, however, is arbitrary when the bin sizes are set to a value of one).
An example of a histogram is below.
Histograms also give a good visual indication of the distribution of the data about a certain point and, when combined with the mean and standard deviation, are easily compared with other distributions of the same data. This makes them ideal for evaluation of data within this project.
Student’s t-test
The two sample t-test is used to determine whether two population means are equal. The most common application of this test is to determine if a new method or action is superior to a current or previous method or action.
The test used two hypotheses, the null hypothesis (“the population means are equal”) and the alternative hypothesis (“the population means are not equal”) of which one is rejected based on a statistical calculation which takes into account the sample mean, sample standard deviation and the sample size. Should the null hypothesis be rejected in favour of the alternative hypothesis, then the population means are different and a statistically significant change has taken place.
Further information on this test, and the formulae used to calculate the relevant parameters can be found at the following website:
http://www.itl.nist.gov/div898/handbook/eda/section3/eda353.htm
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R Squared Value
The Linear Regression R-Squared10 function determines the degree of a linear relationship of a field to time over a given period of time using the square of the Pearson product moment correlation coefficient. The Pearson product moment correlation coefficient is typically represented by the letter r. The square of its value has a range from 0 to 1 where:
1 = Perfect Positive or Negative Correlation
0 = No Correlation
Outliers
The removal of outliers from data should only be done following a detailed analysis of the data and its meaning. Outliers can hold important information especially with regards to traffic flow conditions. Unfortunately situations can, and have arisen, where some data points are not truly representative of the actual journey times for a number of reasons: ♦ a vehicle may pass the first node in the link and make smaller journeys in between the nodes before exiting some time later thus not taking the direct route through the link as expected (e.g. a courier van); ♦ a vehicle may stop at some point within the link before continuing with its journey sometime later adding the stationary time to the overall journey time (e.g. a HGV); ♦ a vehicle may be inherently slow moving (e.g. a wide/escorted load); and, ♦ the software system used to calculate the journey times would return values which were preceded or followed by system downtime (this was found during system malfunctions and or updates). Furthermore, many outliers were found to occur in the early hours of the morning. These are unlikely to be indicative of a build up of queuing traffic, and are atypical of the underlying traffic conditions at the time.
The method chosen to remove the outliers uses an assumption of normalcy which does not strictly apply to journey time distributions as they are inherently periodic. However, the outliers that required removal were particularly large and did not reflect the journey times that the study was interested in measuring. Given the size of the samples, it was not practical to use visual methods to remove outliers, so a systematic method was required – this compares the journey time point to a threshold value.
The data were checked following outlier removal to ensure that under no circumstances were journey times removed that may have been a result of congestion or queuing traffic. Additionally, the method was checked to ensure that it was not overly sensitive to the threshold values used. In all cases, the number of outlying data points removed was between 1 and 10 which represents less than 0.1% of the sample size.
10 http://www.le.ac.uk/bl/gat/virtualfc/Stats/regression/regr1.html
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The first step was to produce a linear regression using the relationship between the number of matches (sample size) and the mean journey time (sample mean). The central limit theorem states that for large samples, the sample mean tends towards a normal distribution. As explained above, these journey times would not tend to a normal distribution, however, this method permitted the software to remove the extreme outlying points.
The journey time is selected as the dependent variable, that is to say it is dependent upon the number of matches used to calculate it. Before allowing SPSS to run the regression, two options are selected. The first is to apply a 95% confidence test on the mean; this produces two columns containing the upper and lower limits for the mean, based on the confidence test. The second option is to save the standardised residuals – which creates a third column in the data named ZRE_1.
The number in the column ZRE_1 details how far from the regression line the value is in factors of standard deviations. I.e., a number of 1.4 in this column indicates the value is 1.4 standard deviations from the regression line through the data points. Using SPSS, we can select and remove cases based on the value in the column ZRE_1.
The following equation was used to remove outliers more than three standard deviations away from the regression line:
− 3 ≤ ZRE _1 ≤ 3 (3)
SPSS then removed values which do not fall within this range thus removing the outliers from the dataset
The threshold level set (at three standard deviations from the mean) was based upon the presence of outliers outside of this range (typically around 20-30 standard deviations) and the evaluation was re-run using a larger range of up to six standard deviations to ensure the results were identical. The actual outlier points removed have been included in the tables below:
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Outliers Removed from Scenario A Data
Link ID Timestamp Journey Time (s) Standard Deviations from Mean
250012 1:30:00AM 1908 25.64 3:30:00AM 1881 25.22 3:30:00AM 1849 24.81 3:30:00AM 1774 23.75 3:30:00AM 1711 22.80 3:30:00AM 1675 22.33
250013 3:30:00AM 3560 47.55
250020 3:30:00AM 2440 18.90 3:35:00AM 2373 18.00 3:30:00AM 2302 17.77 3:30:00AM 2101 16.02 3:30:00AM 2108 15.59
250023 3:30:00AM 2965 32.06 3:40:00AM 2939 31.84 3:30:00AM 2226 23.98 3:30:00AM 2136 22.99
250025 10:50:00PM 652 22.28 11:55:00PM 652 22.28 8:05:00PM 629 21.37 12:45:00AM 597 20.14
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Outliers Removed from Scenario B Data
Link ID Timestamp Journey Time (s) Standard Deviations from Mean
250012 1:40:00AM 3447 45.64 1:25:00AM 3129 41.31 9:15:00AM 1670 21.40 9:15:00AM 1670 21.40 9:10:00AM 1577 20.13
250013 12:45:00AM 2695 40.57 12:50:00AM 2695 40.57 12:55:00AM 2695 40.57
250020 3:30:00AM 2039 16.74 1:25:00AM 1980 16.47 1:30:00AM 1980 16.47 1:35:00AM 1980 16.47 3:30:00AM 1979 15.68
250023 5:45:00AM 730 19.75 6:40:00AM 709 19.95
250025 1:20:00AM 3422 34.29 1:25:00AM 3422 34.29 10:00:00PM 2072 20.62 10:45:00PM 1910 18.98 4:40:00AM 1872 18.59
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Appendix B – ATC Volume Charts
This appendix contains the scatter plots produced from the volume data at each ATC site in the evaluation area. A line has been drawn through the points in an effort to identify any likely trends throughout the evaluation.
ATC 1 – Sheffield Parkway from the City Centre
The chart indicates a large increase in the volume of traffic on the Sheffield Parkway during the evaluation with the overall increase of the order of 4000 vehicles per day between September 2007 and March 2008. The value of R squared on the chart of 0.751 indicates a positive correlation (increase) in the data points.
ATC 2 – Sheffield Parkway towards the City Centre
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The chart representing the volume of traffic on the opposite carriageway also indicates the volume of traffic has increased over the evaluation period. Again, the order of increase is approximately 4000 vehicles per day, which would be expected if those additional vehicles are commuter or recurring journeys. The correlation is indicated as positive by the R squared value of 0.563.
ATC 3 – Mosborough Parkway from the Sheffield Parkway (and City)
The volume of traffic using the Mosborough Parkway appears to have remained consistent through the evaluation period. The low value of R Squared suggests there is no real correlation between the data points, positive or negative leading to this conclusion.
ATC 4 – Mosborough Parkway towards the Sheffield Parkway (and City)
The volume to the city centre provides an interesting plot. A clear increase is shown in mid November through to mid December, which coincides with the high level of
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queuing on the M1 northbound and the change in flow profile at Junction 33 due to the road works. It is possible that many users diverted off the M1 at Junction 31 and used the Mosborough Parkway as a diversion to avoid the queues thus increasing the volume for a small period.
The volume of traffic using the Mosborough Parkway towards Sheffield has since reduced to levels seen in September 2006. The hypothesis that the road works on the M1 northbound were affecting volumes on this road seems to have been borne out by the higher rate of increase during the works and the return to normal following the opening of the new road. The best fit line gives the impression of a large increase but this is bias towards the higher than normal values during November. The value of R squared is low which suggests if there is any correlation it is a weak positive one.
ATC 5 – Sheffield Parkway towards Sheffield from Junction 33
The best fit line in the chart suggests an increase over the evaluation period, however the low value of R squared suggests the correlation is weak at best. It is not therefore possible to conclude with any certainty that the volume of traffic has increased significantly at this site.
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ATC 6 – Sheffield Parkway towards Junction 33
The volume of traffic using the Sheffield Parkway in the opposite direction has also remained consistent. A small increase is seen in November but this likely to be diverting traffic that had used the Mosborough Parkway in an effort to avoid the road works northbound at Junction 31. The very low value of R Squared indicates there is no correlation at all between the points, and therefore no increase or decrease.
ATC 7 – Rotherway Northbound from Junction 33
The volume of traffic using the Rotherway northbound has increased of the order of 1000 vehicles during the evaluation. More importantly, the data suggests the volume of traffic has remained consistently high since the turn of the year during Scenario B whereas it appeared to fluctuate regularly between September and December 2007. The value of R Squared, whilst relatively low, does suggest a positive correlation.
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ATC 8 – Rotherway Southbound towards Junction 33
The chart indicates the volume of traffic using the Rotherway towards Junction 33 has remained steady at approximately 13000 vehicles per day throughout the evaluation period. The value of R squared is significantly low suggesting no correlation, and therefore no increase or decrease in traffic volume.
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Appendix C – Journey Time Histograms
The following appendix contains the histograms of journey times for Scenarios A and B. The mean and standard deviation from each histogram have been included in the main report. There are three histograms for each link representing all data collected, all data collected during peak evening hours and all data from Friday peak evening hours.
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C 1 – Sheffield Parkway to Rotherway Scenario A All Data
C 2 – Sheffield Parkway to Rotherway Scenario B All Data
The mean journey time across this link has increased; however, this increase is not evident on the distributions as the peak frequencies appear to be in the same position. The increase in the number of observed journeys under the mean journey time in C2 account for the increase in the standard deviation calculated. The tails for each distribution extend to the same length which demonstrates drivers have not had their journey time extended through the implementation of ITM.
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C 3 – Sheffield Parkway to Rotherway Scenario A All PM Data
C 4 – Sheffield Parkway to Rotherway Scenario B All PM Data
The distributions for PM data are also very similar in shape. A smaller number of journeys observed in Scenario B above 200 seconds have resulted in a reduction of the standard deviation despite the tails of both distributions extending to above 400 seconds.
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C 5 – Sheffield Parkway to Rotherway Scenario A Friday Peak Data
C 6 – Sheffield Parkway to Rotherway Scenario B Friday Peak Data
The increase in the standard deviation between the above scenarios can clearly been seen as a result of the number of higher duration journeys observed in Scenario B. There are no comparable journeys within distribution C5 to skew the standard deviation. In this example the calculation of the standard deviation can be misleading as it gives the impression of reduced reliability based upon a very small
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number of journeys. Given that the frequency of these longer journeys is never larger than 1, it is possible these journeys are not truly representative of conditions within this link. If the frequencies were higher, then repeated journeys of a similar nature would indicate repeating conditions giving confidence the standard deviation change is a true reflection of the effects of ITM.
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C 7 – Rotherway to Sheffield Parkway Scenario A All Data
C 8 – Rotherway to Sheffield Parkway Scenario B All Data
Distribution C8 shows a significant increase in the standard deviation of the journey times. Furthermore, this increase is not the result of randomly observed journeys as seen in C6, and seems indicative of conditions within this link. The sharp distribution
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in C7 has been replaced with a smoother, larger distribution extending to much larger journey times and containing a greater variation within its limits. More journeys are observed to be taking below 50 seconds to complete which will explain the reduction in the mean journey time.
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C 9 – Rotherway to Sheffield Parkway Scenario A All PM Data
C 10 – Rotherway to Sheffield Parkway Scenario B All PM Data
The increase in the standard deviation between the two distributions above is a result of the visible increase in the frequency of journey times of a greater range than that observed in Scenario A (C9). There is a lower frequency of journeys at the mean
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journey time in C10 despite the larger sample size; however, the mean journey time is clearly shown to reduce by the shift in the peak of the distribution. A significant number of journeys have been observed which appear to take less than 50s to complete which will also account for the reduction in the mean and the increase in the standard deviation.
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C 11 – Rotherway to Sheffield Parkway Scenario A Friday Peak Data
C 12 – Rotherway to Sheffield Parkway Scenario B Friday Peak Data
The distribution in C11 is very sharp and well distributed about the mean. In C12, the distribution has become much more spread about the mean and this has resulted in a large increase in the standard deviation. Although the mean has reduced, the
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distribution in C12 is not about one particular value, as there appears to be two peaks. Given the range of values, and the frequencies of them, the increase in the standard deviation is not a result of sporadic journeys and is indicative of a reduction in journey time reliability within this particular link.
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C 13 – Sheffield Parkway (Parkway Markets towards Junction 33) Scenario A All Data
C 14 – Sheffield Parkway (Parkway Markets towards Junction 33) Scenario B All Data
The peaks of the above distributions are in the same place. The higher peak in C14 is a result of the larger sample size. The similarities between the distributions are reflected in the similar values of the standard deviation. C14 shows a larger number
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of journeys lasting less than 200s which may account for the reduction in the mean journey time.
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C 15 – Sheffield Parkway (Parkway Markets towards Junction 33) Scenario A All PM Data
C 16 – Sheffield Parkway (Parkway Markets towards Junction 33) Scenario B All PM Data
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The larger peak in C16 is a result of the larger sample size. The position of the peak shows that the mean journey time has reduced slightly. The peak in C16 is very sharp when compared to C15. This indicates an increase in reliability, in that fewer journeys are distributed away from the mean, despite the increase in the standard deviation. This increase in standard deviation would indicate a reduction in the reliability of journey times which is not the case.
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C 17 – Sheffield Parkway (Parkway Markets to Junction 33) Scenario A Friday Peak Data
C 18 – Sheffield Parkway (Parkway Markets to Junction 33) Scenario B Friday Peak Data
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The reduction in the standard deviation is evident in the visual change in the distribution between C17 and C18. The peak in C18 is much sharper indicating a definitive mean journey time with few journeys observed outside of this mean. In C17, there was a greater variation in journey times about the mean so the reliability of journey times has increased within this link.
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C 19 – Sheffield Parkway to M1 SB on-slip Scenario A All Data
C 20 – Sheffield Parkway to M1 SB on-slip Scenario B All Data
The distribution of journey times in C20 shows a reduction in the mean in that the peak has shifted to the left. Also evident is that the number of journeys taking place below the mean has increased slightly. The reliability of journey times on this link
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has increased as demonstrated by the shorter tail on the distribution in C20 than that in C19. In Scenario A, many more journeys taking longer than 200s were observed which has resulted in a large reduction in the standard deviation.
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C 21 – Sheffield Parkway to SB on-slip Scenario A All PM Data
C 22 – Sheffield Parkway to SB on-slip Scenario B All PM Data
The reliability of journey times on this link at this particular time has increased. This is demonstrated by the large reduction in the standard deviation, and also by the significant change in the distribution as shown in C22. The distribution in C22, and in
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C20 also indicate that journeys are now not taking longer than 200 seconds adding further evidence to the increase in the reliability of journey times.
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C 23 – Sheffield Parkway to SB on-slip Scenario A Friday Peak Data
C 24 – Sheffield Parkway to SB on-slip Scenario B Friday Peak Data
The distributions in C23 and C24 show the mean journey time has decreased for this particular link and time period. The standard deviation has increased which suggests the reliability of the journey time has decreased however closer inspection reveals
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that more journeys are observed taking less than 50s thus increasing the spread of the journey times observed and skewing the standard deviation. No journeys have taken longer than those observed in C23 indicating the reliability has not decreased despite the suggestion from an increased standard deviation.
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C 25 – Rotherway to SB on-slip Scenario A All Data
C 26 – Rotherway to SB on-slip Scenario B All Data
The distribution in C25 is very sharp and its width is very small. This is reflected in the small value of its standard deviation. The distribution in C26 is wider and has a long tail where higher duration journeys have been observed, however, the mean
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journey time has reduced and a high proportion of journeys, as demonstrated visually by the distribution, are of mean duration. The increase in the standard deviation is misleading as it suggests that journey time reliability has decreased by a factor of three. Mathematically this may be the case, but given the distribution shows a small number of points of high duration the standard deviation is skewed by the small number of longer journey times giving the impression reliability is much worse than in Scenario A when in reality it may have been congestion causing the observations and skewing the calculation.
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C 27 – Rotherway to SB on-slip Scenario A All PM Data
C 28 – Rotherway to SB on-slip Scenario B All PM Data
The distribution in C27 is tightly distributed about the mean, whereas in C28 the distribution is much wider. This has resulted in an increase in the standard deviation of the journey times. The range of journey times observed in C28 is much greater
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than that of C27, and furthermore, a large proportion of observed journeys have a duration under the mean time of scenario A. Visually, the distribution in C28 is wider and smoother than in C27 which indicates less reliability.
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C 29 – Rotherway to SB on-slip Scenario A Friday Peak Data
C 30 – Rotherway to SB on-slip Scenario B Friday Peak Data
The distribution in C30 shows a clear reduction in the reliability of journey times experienced on this link for this particular period of observation. A distribution about the mean time is evident in C29, whereas in C30 no clear peak is defined.
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Furthermore, a larger range of journey times has been observed in Scenario B as signified by its width adding further evidence for this reduction in journey time reliability.
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Appendix D – Traffic Signal Controller Configuration
Introduction
This technical note records the configuration of the traffic signal controller and the parameters set for the operation of ITM at M1 Junction 33 and is peculiar to the traffic conditions and topographical layout of that junction and were correct as at 8 February 2008.
System Overview
The traffic signal controller for the roundabout gyratory is a Siemens type TS800. The Peek ramp metering system relays values associated with slip road queue lengths to the traffic signal controller. This information is transmitted via a one way wireless link with transceivers located at the nearside entrance to the southbound on-slip and on the nearside circulatory traffic signal pole at the northbound off-slip node.
Ramp Metering Controller Configuration
The ramp metering system has several queue loops located in each lane of the southbound on-slip between the slip road entrance and the ramp metering stop line. Every 10 seconds, the average occupancy of the loops is calculated (parameter named: oDesCq) and reported as a percentage value.
The ramp metering controller will pass to the traffic signal controller four data bits when certain conditions exist as detailed below. The threshold values are set as stated below. ♦ RM_ON – when traffic conditions on the mainline carriageway of the motorway satisfy the ramp metering system parameters necessary for ramp metering to become operational (the upstream lane one speed is low enough to permit safe merging for vehicles and the downstream occupancy equates to the preset critical occupancy value indicating the onset of congestion). ♦ RM_Q1 – oDesCq exceeds set point 1 (40% average occupancy - small queue on the slip road). ♦ RM_Q2 – oDesCq exceeds set point 2 (50% average occupancy - medium queue). ♦ RM_Q3 – oDesCq exceeds set point 3 (60% average occupancy - large queue). Traffic Signal Controller Configuration
During normal operation of the gyratory, the signals run three sets of CLF timings based on AM peak conditions, off-peak conditions and PM peak conditions.
The timings for these CLF plans will change when: ♦ the off-slip queue loops detect the presence of a queue; and, ♦ the receipt of the ramp metering bits (RM_Q1, RM_Q2 and RM_Q3) indicate that a significant queue exists on the southbound on-slip
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For each set of CLF timings there are a further three sub sets of plans, which are activated on receipt of queue loop inputs as follows:
Morning Peak CLF Plans: ♦ PLT0: Plan 0: Normal operation no queue loop inputs ♦ PLT1: Plan 1: Northbound Q loop input ♦ PLT2: Plan 2: Southbound Q loop input ♦ PLT3: Plan 3: Northbound and southbound Q loop inputs Off Peak CLF Plans: ♦ PLT4: Plan 4: Normal operation no Queue Loop inputs ♦ PLT5: Plan 5: Northbound Q loop Input ♦ PLT6: Plan 6: Southbound Q loop Input ♦ PLT7: Plan 7: Northbound and southbound Q loop inputs Evening Peak CLF Plans: ♦ PLT8: Plan 8: Normal operation no Queue Loop inputs ♦ PLT9: Plan 9: Northbound Q loop Input ♦ PLT10: Plan 10: Southbound Q loop Input ♦ PLT11: Plan 11: Northbound and southbound Q loop inputs The ramp metering bits are received at the traffic signal controller on I/O Port 1 in the following configuration: ♦ Det 8 Port 1 Bit 0 – RM_ON ♦ Det 9 Port 1 Bit 1 – RM_Q1 ♦ Det 10 Port 1 Bit 2 – RM_Q2 ♦ Det 11 Port 1 Bit 3 – RM_Q3 The traffic signals have been configured to react to the receipt of the RM_Q bits. On receipt of any RM_Q bit, the relevant special conditioning timer will be set in the traffic signal controller, which, when expired, terminates the respective green of the traffic signal controller phase. At present, only the Parkway and Rotherway approaches have been configured to have their green times curtailed with Parkway the only approach currently enabled. The value of the special conditioning timer varies depending upon the RM_Q bit being returned, with a lower timer value being given to the RM_Q3 input, when compared to a RM_Q2 input, which in turn is lower than the RM_Q1 input.
For details of the exact values of the special conditioning timers refer to the controller datasheets and any temporary data held in the controller. The special conditioning timers currently set up are PIR44 for RM_Q1, PIR45 for RM_Q2, PIR46 for RM_Q3 and PIR47 for the phase prevent period, all for the Parkway approach.
The controller was validated on the 8 February 2008 with the special conditioning timers set as follows:
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♦ Parkway receives 38 seconds of the cycle time extended by bonus green to 43 seconds if the circulating traffic detector demands drop out. RM_Q1 limits the bonus green to a total of 39 seconds per cycle; ♦ RM_Q2 limits the green to 35 seconds; and, ♦ RM_Q3 limits the green to 30 seconds. Typically RM_Q3 only triggers twice in the peak period thereby only affecting the operation of the signals for two signal cycles.
Maintenance Implications
The junction controller is fitted with a short range wireless link receiver which inputs the RM bits described above to the ST800 controller. This receives data via a radio unit (black) fitted to the (A phase) circulatory nearside pole,
The site is linked to the Sheffield UTC system using a Peek Chameleon Unit with TCP/IP communications over ADSL via the Zyxel router. The router also provides communications for two wireless CCTV cameras mounted on lighting columns on Parkway and Rotherway via a wireless access point (with white aerial), again mounted on the nearside circulatory pole. These are the responsibility of Sheffield UTC to maintain.
For the CLF plans to continue to be active, it is essential that the appropriate CFE command has been set correctly. This is CFE8=1.
For the traffic signals to react to RM_Q bits it is also essential that the appropriate CFE commands have been set up for the respective approaches which have their greens curtailed. Currently this is CFE3=1 for the Parkway approach.
For the off-slip road queue loops to continue to operate within CLF, it is also important that any temporary data relating to the call and cancel times of the Q loops is not lost or amended. Refer to the controller datasheets and temporary data for the respective values. (DCLn for the call time and DCNn for the cancel time). The queue function will only work if both the Q loops in each lane are called. So any changes must be done to both pairs of queue loops. e.g. PLOOP1 and PLOOP2 are for northbound nearside lane. The PLOOPS are set to fail inactive under DFM and must never be set active.
The special conditioning timers 0 and 1 are set to 60 (PIR0 and PIR1) as this is the cycle time for the queue clearance plans.
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Appendix E – Scenario A Traffic Trends
Motorway Conditions during the Evaluation Period
To obtain an indication of the impact of the widening scheme and the flow of vehicles to Junction 33, the vehicle flow data for loop sites 4551A (northbound towards Junction 33) and 4567B (Southbound towards Junction 33) were used to plot a simple scatter graph of average hourly vehicle flow across the evaluation period from September 2007 to March 2008. Average hourly vehicle flow for a 24 hour period and 12 hour daytime (7am – 7pm) period was also plotted for comparison. The charts are simple representations of motorway flow data to gain a general picture of the conditions on the motorway and do not take periodicity into account.
Northbound Analysis
The ITM Pilot Project is concerned solely with the southbound ramp metering site and the traffic using the roundabout hence northbound traffic is unaffected by its implementation. However, the northbound traffic entering the evaluation area has been affected by major changes to the M1 throughout the evaluation and may have altered driver behaviour entering and leaving Sheffield. In an effort to assess any impacts, the northbound carriageway has been analysed.
Loop site 4567B – Southbound
E 1 – 24h Average Flow
The best fit line for the chart indicates a reduction in the average hourly flow southbound towards Junction 33, and suggests that the flow levels are lower after the removal of the road works. However, the range of the data after 21st December is within the range of the data whilst the road works were in place, and the apparent decline in flow may not be significant.
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E 2 – 12h Average Flow
Analysis across the 12 hour period also shows the same apparent decline in hourly traffic flow as that seen in E 2. The range in flow over 12 hours seen after the end of the road works is also within the range of that whilst the road works were in place, so it is not clear that any change in flow is likely to be significant.
Loop site 4551A – Northbound
E 3 – 24h Average Flow
A line of best fit has been applied to the data in E 3 which suggests the average hourly flow of traffic has neither increased nor decreased over the evaluation period. The flow data after the end of the road works is not noticeably different to that during the road works suggesting that the road works did not have a major effect on the flow experienced at this loop site.
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E 4 – 12h Average Flow
The chart E 4 indicates that during peak daytime hours (7am – 7pm) the average hourly flow rate for each day does not deviate from around 4000 vehicles per hour as indicated by the best fit line. Similarly, the group of data collected after the end of the road works does not differ visually from that collected whilst the road works were in place.
Seasonal Variations
Since Scenario A and Scenario B source data from different seasonal periods of the year, it is likely traffic patterns will be naturally different, despite the indications from the loop analysis that motorway flows have not changed significantly throughout the evaluation.
Widening Works
In order to ascertain if traffic entering the local road network from the motorway was affected by the widening scheme restricting the arrival of traffic at Junction 33, the MIDAS loops upstream of Junction 33 were used to plot the average time of peak flow arrival (E 5) and the average hourly flow between 05:00 – 11:00 (E 6)
MTV analysis at Junction 31 northbound showed much larger queuing from 12th November which was the result of a significant change in the traffic management on approach to the road works. The road works were removed on the 21st December 2007. This information has been overlaid on both charts for comparison.
Chart E 5 shows a significant delay in the peak flow arrival following the 12th Nov where peak flow was delayed by up to two hours in one particular week. Once this restricting effect was removed, the time of peak flow arrival began to return to its original time.
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The flow data indicates that a significant drop was experienced at the time of the traffic management layout change and fluctuated below 5000vph during this period. Again the original level of flow returned gradually following the opening of the works.
These charts show a significant change in the arrival patterns at Junction 33 during these road works, and may have influenced driving and/or working practices of road users. For this reason, use of any data in the evaluation between November and January was avoided.
Peak Flow on Junction 33 Approach
M1 J33 Northbound Average Peak Flow Arrival
10:00
09:00
08:00
Time (hh:mm) 07:00
06:00 M1 J31 - J32 Widening Scheme In Progress Roadw orks TM Change Severe Widening Scheme Opened Delays at J31 Northbound
05:00
07 07 07 07 07 07 07 07 07 07 07 07 07 07 07 08 08 20 20 9/20 0/20 1/20 2/20 /10/20 /11/20 /12/20 /01/20 03/09/2010/0 17/09/2024/09/200701/1 08/10/2015/10/ 22 29/10/2005/1 12/11/2019/11/200726 03/12/2010/12/ 17 24/12/200731/1 07/01/2014/01/200821 Week Commencing
E 5 – Northbound Peak Flow Arrival
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M1 J33 Northbound Average Hourly Flow
6000
5000
4000
3000 Flow (vph) Flow 2000
1000 M1 J31 - J32 Widening Scheme In Progress Roadw orks TM Change Severe Widening Scheme Opened Delays at J31 Northbound
0
7 7 7 7 7 7 7 7 7 7 7 7 7 8 8 0 0 0 0 0 0 00 00 00 00 /20 /2 /200 /20 /2 /2 /20 /20 /200 /20 /200 /200 /20 /2 /200 9 0 0 2 09 /09 10 /10 11 /11 /12 /12 12 01 /01 3/0 0/ 7 1/1 8/ 5 9/1 5/ 2 6/11/20073/1 0 7 1/ 7/ 4 1/01/2008 0 1 1 24/09/20070 0 1 22/10/20072 0 1 19/11/20072 0 1 1 24/12/20073 0 1 2 Week Commencing
E 6 – Northbound Average Hourly Flow
Journey Time through Junction 33
The average journey time through Junction 33 was calculated using MTV and plotted for the northbound and southbound carriageway for Scenario A data. A direct comparison was made with the same data following the activation of ITM to assess if southbound journey times along the motorway through the junction have been affected by its implementation. Since ITM has no effect on the northbound exit, this exercise further helps assess the impact of the M1 widening scheme.
E 7 – Mean Journey Time Northbound
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E 8 – Mean Journey Time Southbound
Local Road Network Volume during Evaluation Period
The volume of traffic recorded by the ATC traffic counting sites in the evaluation area was collated and plotted using the same method as used above for motorway flow above. The output charts can be found in Appendix B.
The only ATC site which indicates a change in traffic volume is the site situated on the Sheffield Parkway near to the city centre (Appendix B, ATC 1 and 2). Here the ATC site is reporting an increase in the volume of traffic entering and leaving the city between the hours of 7am and 7pm. This increase has not been attributed to any constraints within Sheffield City Centre and must therefore be considered a natural increase in local traffic volume.
An increase in traffic volume during November is reported from the ATC site on the Mosborough Parkway towards the Sheffield Parkway which then returns to stable levels at the beginning of the New Year. (Appendix B, ATC 4) This is likely to be caused by the higher levels of queuing on the M1 northbound carriageway and drivers have used the Mosborough Parkway as a diversion route north to Junction 33 or Junction 34.
All other ATC sites show that during the period of evaluation the overall volume of traffic on the local road network has not measurably increased or decreased during daytime hours despite natural fluctuations due to periodic and aperiodic changes.
Journey Time Data
For each link in the ANPR system, the histogram of journey times was generated for three distinct periods: ♦ 24h across all days;
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♦ peak hours across Monday to Thursday (to coincide with usual hours of ramp metering operation) between 13:00 and 20:00 hours; and, ♦ peak hours for Fridays only to account for weekly periodicity. To mitigate the effect of outliers on the data values, the mean and standard deviation of journey times were calculated following outlier removal. The method of removing outliers using a statistically robust approach is described in Appendix A.
Table E 1 shows the mean and standard deviation of the journey times. Following the activation of ITM, a comparison between the values will be performed to assess the impact of ITM on journey times within the ANPR links.
The histograms generated from the data are presented in Appendix C.
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Table E 1 – Scenario A Journey Time Statistics Link ID Period Mean Std. Dev. (secs) (secs) 250012 – Sheffield 24h - All Days 101 22 Parkway to Peak - Monday to Thurs. Rotherway (North 110 29 Across Junction 33) Peak - Fridays Only 104 13 250013 – 24h - All Days 72 17 Rotherway to Peak - Monday to Thurs. Sheffield Parkway 84 18 (South Across Junction 33) Peak - Fridays Only 81 11 250020 – Sheffield 24h - All Days 280 30 Parkway Markets Peak - Monday to Thurs. to Sheffield 293 59 Parkway (West to Junction 33) Peak - Fridays Only 293 42 250023 – Sheffield 24h - All Days 269 55 Parkway to M1 Peak - Monday to Thurs. Junction 33 307 83 Southbound Slip Road Peak - Fridays Only 295 57 250025 – 24h - All Days 85 43 Rotherway to M1 Peak - Monday to Thurs. Junction 33 107 58 Southbound Slip Road Peak - Fridays Only 93 27
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Appendix F - Lessons Learnt Report
1. Introduction
1.1 Purpose
A separate document has been produced which is a review of the Integrated Traffic Management (ITM) Pilot Project and details the lessons learnt from it. This appendix is reproduced from that document and highlights some of the project issues which arose, and are likely to arise on subsequent projects of a similar nature, and gives guidance for the future.
1.2 Governance
The project was sponsored by the Highways Agency and was managed through a Steering Group which included Sheffield City Council and Rotherham Metropolitan Borough Council as equal partners. Other contractors and agents of the main parties participated in the Steering Group.
1.3 Background
The Pilot Project in South Yorkshire followed a period of micro simulation modelling and feasibility work which provided the basis for the scheme trial. The Pilot Project began in September 2006 and was concluded with the publication of this evaluation report.
Rotherham MBC is the highway authority for the M1 Junction 33 roundabout and Sheffield City Council operates the junction on its behalf. The Highways Agency maintains the signals through its maintenance agent, CarillionWSP who in turn sub- contract the specialist signal maintenance to Peek.
At the start of the project, the officers of Rotherham MBC expressed concern about the Highways Agency’s proposals to install ramp metering on the southbound motorway on-slip road of the M1 at Junction 33 and the potential effects this would have on local traffic. Concurrently, this site was also being considered by the Highways Agency for an ITM pilot site to link traffic signal control on the local roundabout to the operation of the ramp metering controller. Rotherham’s officers were more inclined to accept ramp metering with ITM as this offered a better approach to improve the management of the network around the junction than ramp metering would in isolation. It was subsequently agreed that this junction would be part of an evaluated pilot project to measure the effectiveness of the ITM concept.
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2. Lessons Learnt
2.1 The Steering Group
It was clear from the outset that it was important to establish a Steering Group for the ITM project as a forum for the exchange of information and equitable resolution of issues arising. This forum included the Highways Agency, Sheffield City Council, Rotherham Metropolitan Borough Council and the Highways Agency’s maintenance contractor, CarillionWSP. The Steering Group met monthly and was one of the key drivers for the project.
The success of the project depended on maintaining good relationships within the project and allowing all views to be expressed and considered.
This chapter discusses some of the issues the Steering Group considered with regard to the management and conduct of the pilot and the methods adopted for their resolution. Whilst some of these issues may be specific to the pilot site, these highlight circumstances which typically arise in a project of this nature which may benefit similar ITM projects across administrative jurisdictions.
2.2 Project Issues
2.2.1 The Evaluation Plan
The pilot project adopted the “Guide for the Design, Management and Delivery of Pilots and Trials on the Highways Agency Network”11. It was essential to plan the evaluation of the pilot project as an integral part of the design process and not as a subsequent activity. Installation of equipment specifically for the evaluation needs to be concurrent with the permanent works for optimum use of resources.
The local authorities were also able to contribute to and comment on the plan and ensure that it was appropriate for evaluating the impact of ITM on the local road network. The plan was reviewed on several occasions as a result of events and changing circumstances. Having a well established plan, it was relatively uncomplicated to accommodate changing circumstances and adapt the approach to data gathering.
2.2.2 Data Collection
The Evaluation Plan clearly set out the parameters which were going to be measured and evaluated. Data collection was therefore defined early, and from August 2007 information was collected from a number of sources identified in the plan.
Raw data files were collected and stored from ANPR cameras locations, MIDAS outstations and traffic counters on the local road network. On arrival, each month’s data file was checked for errors before being stored as processed information in a harmonised format necessary for the subsequent evaluation. A log was kept of all
11 “Guide for the Design, Management and Delivery of Pilots and Trials on the Highways Agency Network”, PR241/06, November 2006
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data sources on a daily basis which enabled us to identify days when information was not typical of normal traffic conditions due to the effects of weather or traffic incidents. It was this planned approach to data collection and processing, established at the outset, which gave us the flexibility to analyse the impact of differing long term events on the network such as the motorway widening contract between Junction 31 and Junction 32 and the widening of West Bawtry Road, an important feeder route from Rotherham to the motorway.
The period necessary to obtain a reasonable number of representative days of data for the formal evaluation is easily underestimated. Other events, planned and unexpected, severely limit the validity and usefulness of much of the data collected. The data collection period therefore needs to be an integral part of the project programme and sufficient time allowed to ensure a minimum of twenty days of representative data can be collected free from traffic anomalies. The ratio of representative days to total data collection days was about 1:4. This will naturally vary from site to site.
2.2.3 Identifying an Equitable Outcome
The success of the project was dependent on all parties being able to recognise the impact of operational changes on the traffic flows within their respective jurisdictions.
This was recognised early in the project and confidence sought through micro- simulation modelling of both ramp metering and ITM traffic signal control. This demonstrated theoretically that the proposed changes were viable, met the project objective and would be acceptable. The results encouraged a positive attitude towards the implementation phase.
The confidence gained from the modelling process enabled Rotherham MBC to report positively to their elected members about the outcomes and progress of the project. On future projects, it is recommended that time is spent to identify the likely outcomes of change to gain support and project participation by local authorities before the start of any design work for installation is begun. The project was sponsored by the Highways Agency and principally funded by them. It follows, therefore, that the Agency must ensure that its own priorities are not dominant in the Steering Group and that the needs and priorities of local authorities are given equal consideration and their concerns properly addressed.
The Steering Group provided an appropriate forum to openly discuss all aspects of the project’s outcome.
2.2.4 Cost Considerations
In a project of this nature there are inevitably issues about cost sharing, funding of project responsibilities and procurement of capital equipment and its ongoing maintenance. This project resolved these issues by creating a Service Level Agreement between Sheffield City Council and Atkins as contractors to the Highways Agency. In exchange for managing the local collection of journey time data, the Highways Agency supported Sheffield City Council to fund the additional ANPR cameras on the local roads linked into the existing central office processing
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computer. It also removed any responsibility for the Highways Agency to install and maintain equipment on roads outside its jurisdiction.
As this was a pilot scheme, the collection of evaluation data was critical and in this instance, an SLA provided a mutually acceptable and equitable solution. As ITM is promoted across the network, the SLA approach will not be relevant as the data collection services are unlikely to be part of these schemes. A mechanism is needed in scheme planning to address the funding of such a joint initiative, especially one in which users of the Highway Agency’s network are perceived to be the principal beneficiaries.
Sheffield also contributed to the project with the free issue of a traffic signal controller, communication equipment and a broadband connection to connect the traffic signal controller to the central operational control room. Both Councils contributed staff time to the project to assist in the project management and coordination of site activities as well as data collection.
2.2.5 Programme Management
The Network Services Directorate and their scheme consultant organises its resources to deliver finite term projects. Local authorities and the Agency’s area offices are committed to day-to-day service delivery. The duties of the latter group (often requiring immediate attention) distract resources which inevitably frustrate the project timescales. This difference in respective organisational orientation needs to be recognised in programme planning. In hindsight, the project had to allow float in the scheme programme to accommodate fluctuating resource availability inherent with service orientated organisations. This was clearly demonstrated when the area became severely flooded during the Summer 2007 when all available resources were concentrated on flood relief in the community and delays to the project had to be accommodated.
Although this project was an Agency funded initiative, in a cooperative and equal partnership, the partners also have priorities to address which may mean the Agency cannot necessarily achieve the timescale goals it would like. However, with the positive attitudes in the Steering Group, realistic programme milestones were achieved which were acceptable to all parties.
2.2.6 Supply Chain Management
On occasions during the installation of technology, relatively inexperienced sub- contractor technical staff arrived on site with minimal knowledge of what was expected of them and with an anticipation of a high level of supervision from the main contractor’s representative. When this person was unavailable which occurred on at least one occasion, there was a risk of abortive work. This was traced to problems in the communication chain whereby initial design drawings and plans were not being copied to the operatives but being retained at a higher managerial level. Procedures were instigated to ensure that site work instructions received by site operatives were the same as those issued to instruct the work.
The site works were scheduled for mid June 2007. However, they were not completed until July largely because of the extensive flooding in the Sheffield area
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Lessons Learnt Report
during late June. This natural disaster changed local priorities and with so many parties involved, disruption to the ITM programme was minimised by having a close working relationship between the members of the Steering Group. This also demonstrated the wisdom of single points of contact throughout the supply chain for managing the unexpected and adapting to the rapidly evolving circumstances.
The organisation of a Steering Group was beneficial in reducing the time taken to recognise and resolve problems which inevitably arise when introducing new engineering concepts.
2.2.7 Improved Maintenance Procedures
At this site, the ownership, operational management and maintenance management were, and remain, the responsibility of different organisations. Prior to the pilot project, this had inevitably led to a lack of ownership for issues and consequently a lack of coordination in the maintenance management of the site and the operational effectiveness of the traffic signal operation. One benefit of the project was to establish more permanent procedures and processes for communication, bringing the site up to date and the continuing assessment of its operational effectiveness.
2.2.8 Sensitivity of Evaluation Parameters
The robustness of the data was a major issue on this project with so many extraneous events affecting the parameters the project wished to analyse. These included the impact of differing traffic management regimes associated with the M1 Junction 31-Junction 32 widening and the long term road works on West Bawtry Road; differing school holiday periods in RMBC and SCC; traffic pattern variation around the Meadow Hall shopping complex in the lead up to Christmas; road works on Sheffield Parkway; long term power failures to critical data collection equipment; and changes to traffic arrival patterns at Junction 33 following completion of various road works.
It was also assumed at the start of the project that the signals were operating at their optimum before introducing ITM. One of the issues identified was that the site had inherent faults which took time to fix and bring the site up to standard before ITM could be assessed.
2.2.9 Qualitative Benefits
Early in the project it was recognised that some of the evaluation parameters defined in the evaluation plan were already very sensitive to external influences. However, in addition to quantifiable benefit discussed elsewhere in this report there have also been qualitative benefits.
The project has been a major success in developing a more cohesive working relationship and clarification of responsibilities for operation and maintenance. In another example, during the validation work and extensive observation on site, lane use was seen as very inefficient and a proposal was made to improve the lane designations and road markings which was not part of the original project remit. These proposals were agreed collectively by the Steering Group to further enhance the operational effectiveness of the junction and adopted by RMBC.
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