BOARD OF INQUIRY BASIN BRIDGE PROPOSAL
Attachments to evidence of John Foster for Save the Basin Campaign Incorporated
Index
Item Page
Traffic Operations in Bottle Necks 001
Transport Models and Intersection Analysis 018 Page 1
Attachment A: Traffic Operations in Bottle Necks
Overview:
1. This technical note provides background data and evidence to support my contention that both the SATURN and S-Paramics models are seriously flawed in that they fail to replicate critically important traffic conditions in the vicinity of the proposal.
2. I have assembled from past studies and direct observations a detailed description of the bottleneck conditions on the approaches to Wellington City and particularly that affect approaches to the Te Aro area. Downstream of the bottlenecks peak hour flows cannot change. This creates a relatively calm and settled traffic environment in the Te Aro area including the Basin Reserve. This will persist unless or until the current RONS programme is delivered and especially until the proposed duplications of the Terrace and Mount Victoria tunnels are completed. Following duplication of the tunnels, pent up upstream demand will be released and in my opinion will have a significant impact on traffic in Wellington City and especially in the Te Aro area.
Modelling Bottlenecks
3. In my view, modellers for the Proposal have not properly addressed the effect of bottleneck conditions on traffic operations. The effective performance of the Wellington Regional arterial network depends primarily on the ability of the major intersections to efficiently cope with everyday traffic demands. Currently many of these critical intersections are overloaded during much of the morning peak periods on weekdays. Bottleneck conditions have been prevalent at Pukerua Bay, Mana Esplanade, Ngauranga Gorge, Petone On Ramp, and Mount Victoria Tunnel for at least the past 10 years. Only those at Mana have been corrected by widening the affected roadways to increase their capacity.
4. In nearly all cases a merge manoeuvre is involved whereby the joining of two of more traffic streams exceeds the capacity of the receiving roadway for a short period. I have personally measured the details of the bottlenecks listed
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above. The following table shows the observed capacity limit, the period over which this capacity is exceeded, and my rough estimate of the peak demand of the incident flows. I have not included the bottlenecks that occur in the Terrace and Mount Victoria tunnels, as these are described in detail later in my evidence. Nor have I included many small period bottleneck situations where capacity limits apply for periods significantly less than 60 minutes.
5. The estimates of likely peak demands have included three components, the excess demand currently stored upstream of the bottleneck, an allowance for the return of traffic diverted to otherwise less desired routes, and an assessed increase due to induced traffic effects. It is unlikely that such latter increases would exceed 5%, but the very substantial reduction in travel times that would accrue should the flow restrictions at Petone and within the Ngauranga Gorge be removed could engender a substantial shift from public transport.
PEAK/ CAPACITY PERIOD PEAK DEMAND LOCATION (veh/hr) DIRECTION (veh/hr) (mins) AM 1,600 50-70 1,700-1,850 SH 1 - Pukerua Bay northbound AM 1,480 80-100 1,950-2,300 SH 1 - Mana Esplanade southbound PM 1,480 100-150 1,900-2,100 SH 1 - Mana Esplanade northbound AM 6,000 95-110 6,500-8,500 SH 1 - Ngauranga Gorge southbound AM 4,000 100-120 5,000-6,000 SH 2 - Petone On Ramp southbound
6. The following section contains a detailed technical description of the real world traffic flow conditions that apply northbound during the morning peak period over the length of State Highway 1 stretching from about midway along Cobham Drive to the Basin Reserve. It is necessary to firmly establish the actual nature of every day traffic events to provide an objective benchmark for the detailed review of the virtual world of the traffic models discussed in later sections of my evidence.
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Characteristics of the Traffic Stream
7. It can be shown with mathematical rigour that the flow of traffic along a uniform roadway is completely described by only three variables flow rate, speed, and density. It is convenient to express flow rate in vehicles per hour, speed as the average speed in kilometres per hour, and density in units of vehicles per kilometre. It can be further shown that these three variables flow rate (q), speed (u), and density (k) are related by the equation - q=u.k .
8. Research by scientists at General Motors Corporation in the late 1950’s showed that if the traffic stream is constrained by disallowing overtaking on a crowded road, that cars follow according to a simple rule. The following car accelerates or slows according to the rate at which the car in front appears to be getting farther or closer to the driver of the following car. The response is then directly proportional to the relative speed between the vehicles and is delayed by the reaction time of the following car-driver combination1.
9. The car following law implies that there exists a direct relationship between two of the fundamental variables in that speed is inversely proportional to the density. In mathematical terms speed equals a constant times the density and the flow rate is proportional to the density squared; or is parabolic in form.
10. The likely relationship of flow rate versus density for a single lane when confined, say in a tunnel; is illustrated in Figure 1 below. The dashed portion identifies that portion of the relation where the necessary conditions of crowding and no overtaking are not met. In these circumstances spacing and headways are not related but are independently random. The data points have been obtained from the TMS site in Ruahine Street described in paragraph 13 below.
1 A reference will be provided to this analysis.
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1800
1600
1400
) 1200
1000
800
Flow Rate (Veh/Hr Rate Flow 600
400
200
0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 Density (Veh/Km)
Figure 1: Flow Rate - Density Relationship
11. The function has a maximum value, termed the saturation flow rate, or simply the capacity. In this case, a flow rate of 1600 vehicles per hour (veh/hr) at a density of 45 vehicles per kilometre (veh/km) with a speed of 35 km/hr. In addition, the relation displays two crucially important properties:
a) For any value of the flow rate less than the capacity there exist two valid states of differing density. For example a flow rate of 1100 veh/hr can exist at a density of 20 veh/km with a speed of 55 km/hr, or at a density of 70 veh/km with a speed of 16 km/hr; b) The densities along the right hand arm are significantly greater than those along the left hand arm of the relation.
12. Real world drivers are conscious of the relative proximity of other vehicles in their lane. Density rather than speed or flow rate has been adopted by the USA Highway Capacity Manual as the determining measure affecting the Level of Service (LOS) of high level facility roadway types Drivers perceive densities
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greater than that of the maximum flow rate as “congestion”, whereas in strict traffic engineering terms congestion occurs only when demands are near or exceed the saturation flow rate.
The Mount Victoria Tunnel Bottleneck
13. Periodically the NZTA traffic monitoring sites are set to record individual vehicle speeds in 15 minute time slices. Observed values are stored in one of 17 speed bins of <30kph, 15 bins at 5kph intervals from 35 to 95 kph, and one when speeds are >95kph. The average speed of the traffic stream can then be monitored throughout an entire day. Figure 2(a) below illustrates such information for northbound flows during the morning peak period on Thursday 17th of August 2012 at the TMS site on Ruahine Street located south of Goa Street. Traffic operations were similar to those described in Figure 2(a) for all the other weekdays of that week.
14. Figure 2(a) shows the counts as a bar graph converted to equivalent hourly flow rates by factoring the 15 minute tallies by 4. The average speed is plotted as the red line referred to the alternate vertical axis located on the right. The density plotted as the solid blue line has been calculated according to the basic formulae by dividing the flow rate by the average speed. The Figure thus depicts the dynamic variations in the three basic flow variables over the period extending from 6:30 am to 9:15 am.
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1600 80
1400 70
1200 60
1000 50
800 40
600 30
400 20 Equivalent Flow Rate (vph) Rate Flow Equivalent
200 10 (vpk) Ddensiy and Speed(kph)
0 0 6:30 6:45 7:00 7:15 7:30 7:45 8:00 8:15 8:30 8:45 9:00 9:15
Volume (vph) Speed (kph) Density (vpk)
Figure 2(a): SH 1 –Northbound (towards CBD) AM Period - Ruahine Street
15. The speed reduces steadily from 60 kph at 6:30 as the flow rate increases then falls suddenly from about 45 kph at 7:30 am to near 20 kph, and remains at this low value until about 9:00 am when it suddenly increases back to near 50 kph. As a direct consequence the density suddenly increases, stays nearly constant for the 90 minutes between 7:30 am and 9:00 am, then falls back to a low normal value. This sudden increase in density and reduction in average speed is typical of the flow conditions associated with bottlenecks when shock waves of suddenly increased densities are transmitted upstream of the capacity limit.
16. The recorded data thus proves that upstream of the count site demands exceed the capacity of the Tunnel over the 90 minutes following 7:30 am. The density and speed changes involved are consistent with the two points on either side of the flow rate density relation of about 1100 veh/hr as discussed above in paragraph 9. Immediately the capacity is reached as the flow climbs the left hand side of the flow rate–density function, the flow regime jumps suddenly across to the corresponding point on the right hand limb of the relationship. In effect the excess demands over and above the capacity limit is stored upstream of the bottleneck over that length of highway needed to accommodate them. Along this section of roadway the high density and low speed will be experienced by all traffic.
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17. In contrast the southbound direction carrying almost the same volume of traffic experiences steady conditions. The average speed and density remain in the range of 50-57veh/hr and 10-25veh/km respectively, as shown in Figure 2(b) below.
1600 70
1400 60
1200 50 1000 40 800 (vph) 30 600 20 Equivalent Foow Rate Foow Equivalent 400
200 10 (vpk) Density and (kph) Speed
0 0 6:30 6:45 7:00 7:15 7:30 7:45 8:00 8:15 8:30 8:45 9:00 9:15 9:30
Volume (vph) Speed (kph) Density (vpk)
Figure 2(b): SH 1 – Southbound (towards Kilbirnie) AM Period - Ruahine Street
18. In cases where the merge bottleneck results from the joining of two separate traffic streams the capacity limit of the receiving roadway is shared between the upstream incident flows. Figure 3 below illustrates the 6:00am to 10:00am ¼ hour Mon-Thurs average variation in traffic flows during the same week on each side of the bottleneck. The site labelled “Tunnel” is located on Patterson Street west of the Tunnel together with that of Ruahine Street illustrated above.
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1800
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1200
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Equivalent Flow Rate (vph) 400
200
0 6:00 7:00 8:00 9:00 10:00
Tunnel Ruahine
Figure 3: Patterson and Ruahine Streets (“towards CDB”) - AM Period
19. Between 7:15 am and 9:15 am flows are essentially constant at 1600 vph on Patterson Street and 1200 vph on Ruahine Street. Consequently, flows from Taurimu Street will also be constant at 400 veh/hr over the same period. Thus the capacity limit condition of the bottleneck is transferred to the joining roadways that then act as bottlenecks themselves. Each produce shock fronts of suddenly increased densities that travel upstream individually to accord with their particular flow-rate density relationships.
Estimated Bottleneck Delays – Mount Victoria Tunnel
20. The NZTA Economic Evaluation Manual describes in Section 3.19 a spreadsheet based procedure for calculating the time variation in delays in cases where the demand exceeds the capacity of a roadway. The method allows calculation of delays provided the demand and capacity is known. A simple trial-and-error based modification of the procedure allows estimation of the demands given the capacity and a sample of the delays as observed in the field. Estimated demand variations for the subsidiary bottleneck in Ruahine Street are illustrated in Figure 4 below. These have been derived based on observed delays on Thursday 22 August 2013. It is emphasised that the estimate is intended to be indicative rather than definitive. A comprehensive series of accurate field measurements over several days and weather conditions was not available.
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1500 16
14 1250 12 1000 10
750 8
6 500 Delay (Mins/Veh) Delay 4
Estimated Demand (veh/hr) Demand Estimated 250 2
0 0 6:00 7:00 7:30 8:00 8:30 9:00 9:30 10:00 Delay Mins /Veh Demand
Figure 4: Ruahine Street Bottleneck Demands and Delays
21. In common with all cases where demands exceed capacity, peak delays are significantly displaced in time with respect to the demand peak. In this example, a peak delay of 8 minutes occurs after 8:00am some 30 minutes after the demands reach their maximum. In fact, delay is not directly related to the flow rate that occurs at the same time. Moreover half of the period of the bottleneck occurs prior to the nominal peak period adopted for the transport models. The peak hourly flow rate occurs in the period 7:00 – 8:00 am; not during the 8:00 – 9:00 am hour assumed by the SATURN and S-Paramics transport models developed by OPUS for the assessment of the Proposal.
22. The estimated peak demand of 1,350veh/hr in Ruahine Street is 14% greater than the capacity limit of 1,185veh/hr. If the same relative increase also applies to the Taurimu Road approach, the actual demand for travel through the Mount Victoria Tunnel could exceed 1,700veh/hr. When the likely return of some 200veh/hr diverted to the alternate waterfront route is added, the actual demand presently wishing to travel through the Tunnel would total at least 1,900veh/hr. Removal of the bottleneck by duplicating the tunnel will coincidentally substantially reduce the travel time and thereby induce a further approximately 4% increase to raise the peak demand to about 2,000veh/hr.
23. On the other hand, should duplication be delayed for 10 years, a modest annual growth of 1% per year could result in an incident demand of some 1485veh/hr in Ruahine Street. This relatively small increase of 10% will
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produce a substantial increase in delays as shown in Figure 5 below. The peak delay then rises to 15 minutes, with the period of serious congestion extending to almost 3 hours from near 6:30am to almost 9:30am. Nevertheless, the flow through the Mount Victoria Tunnel will remain steady at near 1,600veh/hr over the extended congested period.
16.0
14.0
12.0
10.0)
8.0
6.0
4.0
Delay (Mins/Veh Delay 2.0
0.0 7:00 7:30 8:00 8:30 9:00 9:30 Year 2021: Year 2011:
Figure 5: Ruahine Street – Future and Present Bottleneck Delays
24. Travel times which I measured from Evans Bay Parade to the Basin Reserve in May 2001 showed delays between 7:40am and 8:30am in the range of 4 and 5 minutes2. A single observation of flow rates taken at the time and using hand held computers revealed an estimated capacity limit of about 1680veh/hr. So peak delays have increased by about 60% and the capacity is slightly lower than 10 years ago. Commensurate changes can be expected in the next decade should traffic demands recover following the recent economic downturn.
Other Bottlenecks on the Northern Approaches to Wellington CBD
25. In contrast to the south-eastern approaches, the northern approaches to the Te Aro sector of the CBD have six points where demands exceed the capacity during the morning peak period on a typical weekday. Regional travellers destined to the Hospital or the Airport along SH 1 from Porirua City and Kapiti Coast District must pass through three of these bottlenecks in sequence at Ngauranga Gorge where the Johnsonville and Newlands On-Ramps joins the route, at the merge of SH 1 and SH 2 immediately south of Ngauranga , and at
2 These measurements were taken as part of a commission undertaken by Traffic Design Group (TDB) for a WCC transport modelling project.
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either the Terrace Tunnel or Waterloo Quay bottlenecks in the City. Alternatively, Hutt Valley residents travelling to the same destinations along SH 2 and SH 1 are required to pass through the long standing bottleneck where the Petone On-Ramp joins SH 2 before those located along SH 1 or the waterfront arterial.
26. I have personally conducted extensive investigations into the operation of all six bottlenecks in the late 1990’s. At that time the Transit NZ traffic counting system installed within the Ngauranga Interchange routinely recorded speeds and tallies at 2 minute intervals. Figure 6 below illustrates this data for Thursday 21st October 1999 (in paragraph 29 below I explain the relevance of this 1999 data set). The count station was located in the 4-lane section immediately upstream of the merge manoeuvre section where four lanes gradually reduce to three. The lanes are numbered from the left facing the direction of travel. Lanes 1 and 2 are on the State Highway 1 over-bridge, and lanes 3 and 4 those of State Highway 2 passing beneath the bridge. The upper diagram in Figure 6 shows the flow rates between 7:00am and 9:00am, while the lower diagram displays the corresponding average speeds at each of the 2 minute intervals of the recording. The horizontal axis is marked in decimal hours, so that 7.40 equates to 7:24am etc.
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Figure 6: Ngauranga Merge Details Southbound AM Peak
27. The data shows that the State Highways 1 and 2 were performing quite differently. A clear shock front occurred on SH 1 at 7:24am introducing a congestion period of 82 minutes extending to 8:50am. Whereas a short congestion period occurred on SH 2 extending from 8:02am to 8:38am. During the time SH 1 was congested both lanes experienced a flow rate of 1,500veh/hr. In contrast the SH 2 lanes were unequally loaded at
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1,200veh/hr and 1,800veh/hr producing a combined flow rate of 6,000veh/hr following the merge.
28. Careful direct observations of traffic operations at the site of the Petone On- Ramp has established that the capacity of this merge is 2,000 vehicles per hour per lane, or 4,000veh/hr in total. Although the two lanes of SH2 immediately beyond the merge point allow a capacity of about 4,400veh/hr a limit of 4,000veh/hr is transmitted upstream from the lower capacity of the two closely spaced low radius horizontal curves located south of Horokiwi Road. South of this restriction SH2 operates at a saturation rate of 4,000veh/hr at some 60km/hr over the entire congestion period of the Petone merge.
29. Some 800-1,000veh/hr exit from the through lanes of SH2 on the Off-Ramp leading to Ngauranga Gorge located a short distance upstream of the count site, leaving some 1,000veh/hr in lane 3 immediately downstream of the exit. This lane is then only partly filled at the junction with the fully loaded SH1 lanes. Consequently, the SH2 lanes do not suffer a capacity limit at the merge. The SH2 lanes consume half of the available capacity simply because most of the time this rate is the incident flow. Only SH1 traffic suffers significant delay at the merge.
30. I have processed the entire records of 1999 so as to display the start and end time of the congestion period of the SH1 lanes upstream of the merge with SH2. The congestion period is defined as the period of time when the density exceeds 50veh/km in either lane. The results are illustrated in Figure 7 below.
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Figure 7: Congestion Intervals Southbound AM Peak Ngauranga Merge
31. Evidently in 1999 congestion generally commenced prior to 7:30 am but ended over widely varying times between 8:30am and 9:15am. The average congestion period in 1999 was 85.4 minutes, with a standard deviation of 20.3 minutes. Thus some 85% of the congestion periods lie in the range 65.1 to 107.7 minutes. A recent speed survey at this site reveals that for the week beginning 25th June 2012 the congestion period averaged 64 minutes within a range of 20 to 110 minutes; a similar range and average as occurred in June of 1999. It would appear then that current congestion levels at the Ngauranga merge have not altered in the intervening 13 years. However, appearances are deceptive when dealing with such traffic phenomena.
32. A complex situation occurs upstream in the SH 1 lanes within the Ngauranga Gorge itself. In an almost parallel manner as that of SH 2 at Petone, the Johnsonville On-Ramp merge with the two through lanes of the Johnsonville bypass is limited by the receiving roadway capacity of 4000veh/hr downstream at the 2-lane over-bridge that crosses SH2. Consequently, delays during the am peak along the SH1 approach to the City are determined by operations upstream of the SH2 merge.
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33. Further south bottlenecks are evident at the Terrace Tunnel and along the waterfront arterial. Apparently the capacity limits at Petone and Johnsonville can supply a greater flow rate than can be accommodated downstream. Figure 8 below illustrates the measured and estimated delays at the Terrace Tunnel on a typical weekday in 2001.
Figure 8: Year 2001 AM Peak Delays Terrace Tunnel
34. The diagram shows the estimated and measured delays on a typical AM peak during 2001. This data was collected as part of the scheming studies for the Inner City Bypass (ICB). Once again, the congested period extends over the entire nominal AM peak period of the SATURN and S-Paramics transport models adopted by the NZTA consultants. Significantly the measurements show clearly that congestion was experienced for a full 90 minutes after the nominal end of the modelled AM peak. Recent casual observations indicate that congestion here routinely extends to these limits today.
35. An alternate route into the City from the north is available along the Waterfront. It would be expected that this route must also congest as traffic diverts to avoid the delays on the preferred motorway route. Figure 9 below sourced from the same ICB study shows that these delays however are slightly less than those experienced on the motorway. However as also would be expected, the congestion intervals are similar.
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Figure 9: Year 2001 Southbound AM Peak Delays Aotea Quay.
36. But the nature of the Aotea Quay bottleneck differs from the merge type on the approaches to the Terrace Tunnel. The capacity limit at Aotea Quay is due to insufficient capacity at the traffic signal at Bunny Street. This signal is the first of the linked group along the waterfront. Little if any delay is experienced at the subsequent intersections within the group along this route. It is estimated that about 20-30% of the traffic choosing the waterfront route diverts from either SH1 or SH 2 at Ngauranga. The relative travel time for the journey along the entire alternate routes is then relevant, not just that portion along the waterfront.
Before and After Flow Regimes
37. Consequently during the critical AM peak, the Te Aro sector of the Wellington City CBD is protected by upstream bottlenecks that ensure flows in the vicinity of the Basin Reserve are limited over most of the 2 hour period from 7:00am to 9:00am. Moreover, these limits have been present for at least a decade and will persist until the Terrace and Mount Victoria tunnels are duplicated. The Te Aro sector intersections will therefore continue to operate at near their current level of service until then. In effect, a series of upstream dams are holding
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back present and future peak traffic surges producing a calm and settled traffic flow environment.
38. In contrast, once the tunnels are duplicated peak hour demands will suddenly increase by releasing the extra demands currently stored upstream of the bottlenecks, redirect trips from their presently less preferred routes, and induce a small component of additional travel. Based on my analysis, the resulting rapid increase in peak hour flows will swamp the Te Aro sector of the CBD causing a sudden substantial and sustained increase in travel times. This effect will be amplified by a sudden release of the present constraint at the SH1/SH2 merge at Ngauranga Gorge following the widening of SH1 to 4 lanes.
39. These contrasting responses consequential on the presence of bottlenecks produce quite differing traffic flow regimes; before duplication (BD) and after duplication (AD) that will require special attention to the manner in which bottlenecks are modelled. Such challenges are the subject of the second technical note attached to my evidence.
017 Attachment B – Transport Models and Intersection Analysis
Transport Models
1. At the outset, it is pertinent and relevant to establish from fundamental considerations, the guiding principles of sound transport models. The brief exposition detailed below has been derived mainly from my direct experience with the application of a wide variety of software packages and an ongoing involvement with transport analysis over the past 40 years.
2. The following set of guiding principles or basic premises is not intended to be exhaustive or constitute a necessary and sufficient group of specification requirements of a sound transport model. Rather, the discussion is aimed at identifying the most important general requirements:
a transport model relies essentially for its predictive power on an ability to anticipate the behaviour of travellers within a transport system whose performance depends on the presence of other travellers and the choices they may take;
fundamentally, transport analysis is concerned with estimating the equilibrium point between supply and demand. That is, as perceived costs in inconvenience and delays rise, demand falls; within particular modes, through individual intersections, on particular links, and therefore by inference, over the whole system to roughly equate to the supply available;
therefore, it is important to accept that if the equilibrium assumption holds in reality, then the equilibrium point itself is determined by perceived values of delay and inconvenience rather that absolute measures of these variables;
proper estimation of the equilibrium point requires that the model must be consistent. That is, the flows on a link or at an intersection must be entirely consistent with the delays and inconveniences such flows will engender on the perceived values of the participating drivers. Otherwise, alternate routes and destinations may be selected causing the flows and consequential delays to adjust accordingly;
also a properly specified transport model must include direct and faithful representations of the complex interactions and feed-backs by which
1 | P a g e 018 equilibrium is achieved. This requirement implies that differing parts of the model need to be consistent in terms of the precision, mathematical form, and the quantitative strength of the feed-back loops.
Transport Model Precision
3. Analytical systems should possess a uniform level of precision throughout the entire process. This is particularly important in transport models based on determining the equilibrium point and where activities are assumed to be concentrated at centroids rather than be dispersed over an area. Concentrated flows to/from the centroid of activities can produce severely imprecise estimation of public transport line accessibility and critical turning movements at the important intersections of the road network model.
4. Varying levels of precision throughout the network representation or aggregation of activities into zones will produce results whose accuracy is determined largely by the crudest level of precision involved. Therefore, it is not cost effective to adopt inconsistent precision levels throughout the analytical process. If greater accuracy is required, an increase in precision must be applied throughout.
5. The necessary form and precision of the model should be rationally determined by careful consideration of:
the decision making process within which the model is embedded;
the range and character of feasible response options;
the nature and accuracy of the necessary output information;
the criteria on which alternate courses of action are being judged.
6. Ideally, the nature of the problem and the process by which a decision is sought should be available in detail before selection of the form and construction of the model. The general nature of the options, and particularly the differences between them, determine the form and accuracy of the model. The nature of the problem and alternate courses of action should also influence the selection of that portion of the real world it is necessary to include in the model.
7. Unfortunately, this ideal situation seldom arises in practical cases. The analyst is more often confronted with the need to adapt or extend an existing model rather than develop an ideal model form from scratch. Nevertheless, the level of precision
2 | P a g e 019 of the variables already included in an existing model is always under the analyst’s control. Specifically, the joint precision of the zoning system and the network representation should be deliberately determined by the nature of, and the accuracy needs of the problem under study.
Design Accuracy
8. Traditional transport models have usually addressed the “design” problem, which essentially aims at proportioning various elements of the transport system to be consistently commensurate with the likely demands for travel on them. In broad terms, this amounts to determining the number and capacity of public transport lines and roadway arterials to be included in the system. Therefore since the quantum of capacity to be added amounts essentially to that of an arterial lane; this determines the necessary accuracy. An accuracy of about half the capacity of a lane would be appropriate.
9. This concept forms the basis of the determination of necessary validation limits and accuracy levels commonly adopted in North America. Strategic level models would then be accurate to within about half the capacity of a freeway lane. A local tactical level model would require an accuracy of about half the capacity of an approach lane to a typical intersection. Generally, the necessary accuracy is determined by link volumes depending on the magnitude of the volume, and thus on the hierarchal classification of the highway type.
10. The needs of evaluation now tend to determine the necessary accuracy. The traditional criterion for accuracy of about half the capacity of one lane is no longer sufficient.
Evaluation Needs
11. Typically, present and particularly future networks will be expected to operate at levels of service (LOS) close to the D/E boundary1; and may in some circumstances be operating near and beyond level of service E.
1 Where level of service ranges from A (best) to F (worst) as defined by the USA Highway Capacity Manual which for purposes of LOS is generally accepted as standard practice for New Zealand.
3 | P a g e 020 12. The traditional engineering freeboard is therefore critically reduced so that demand level estimates and the proper identification of the precise performance of the design must now be undertaken with greater precision. The level of accuracy now required relates to identifying small demand shifts which may crucially impact on the performance of the roadway elements and intersections. Invariably, variations in demand that occur over short time intervals will require to be identified.
13. In the following, three general levels of precision are identified. Then the necessary precision of the network and activity system that honours the consistency guidelines is specified. Finally, the implied accuracy available for each precision level is estimated.
Precision Levels
14. Three general levels of precision arise as a consequence of the detail to which delays are calculated at intersections:
Level 1 - The traditional level of precision, whereby network supply functions occur on the links or partly on the links and at the intersection as a whole;
Level 2 - Intersection delays are calculated on each approach to the intersection;
Level 3 - When delays occurring in the network are calculated lane by lane on the links and according to each turn on each approach to the intersections.
15. Accuracy increases with greater precision from about + or - half a lane capacity at Level 1, through 100-150 vph for Level 2, to 30-50 vph by turns for Level 3.
16. The needs of consistency dictate that other aspects of the supply and demand side of the model are represented by correspondingly increasing levels of precision. Specifically,
the general level of activity in each traffic zone;
details of the accessibility paths to public transport lines and arterial roadways
the number of real-world streets and intersections directly represented in the model;
the time period of the analysis;
the extent to which parking facilitates need be directly represented;
4 | P a g e 021 would require appropriate levels of precision for consistency and uniformity.
Activity Levels
17. The general level of activity in terms of the number of trips generated and attracted at each traffic zone should be similar and at a precision level consistent with the remainder of the model. Each traffic zone should contain the same number of activities as represented by the weighted sum of the households, general employment not retail, and retail employment with the following weighting factors:
households - 1.0;
non-retail employment - 1.2;
retail employment - 3.0-5.0.
18. Special zones such as the port, airport, hospitals, and tertiary education institutions should be sub-divided to produce a similar quantum of demand as that of general zones. The resulting sub-zones should be connected to representations of real world public transport facility details, driveway and parking arrangements in accord with the precision level details described below.
Centroid Connectors
19. While the number of centroid connectors will vary according to the precise layout of the traffic zones, the average number should reduce as the level of precision increases. Network models adopting level 1 precision will generally have about four centroid connectors per zone; while those of level 3 would have on average of slightly less than two.
Street Network Precision
20. Generally, the number of streets represented one to one in the network model does not vary greatly in models of varying precision levels. All roads with a significant arterial function should be included. No gain in accuracy occurs in including local streets within large traffic zones where only one centroid must be connected to them. Rather, the centroid connectors themselves represent the local street in such situations.
5 | P a g e 022 21. It is wise and prudent to include future traffic zones, sub-divisional patterns, and major driveways within the base network to a similar precision as those now existing. The base network will then contain traffic zones producing zero demands in the base year.
22. Note: If the future representation is to display the same level of precision as the calibrated and validated representation of the base case; future cases involving more activities must possess proportionally more traffic zones.
Analysis Time Period
23. The time period of analysis or the span over which the demands represented by the trip matrix occur should increase in precision in conformity with other aspects of the model. The required level of precision will be determined by evaluation accuracy rather than that needed for assignment.
Assignment Precision
24. Assignment precision is determined by the necessary assumption that drivers’ perceptions of utility remain constant over the analysis time period. Since such judgements as to the best route, or the preferred destination, are imprecise, long time periods (within which traffic volumes vary) could be adopted. If only small variations in perceived delays and inconveniences occur over a 24-hour period, the whole day could be properly included. But this situation cannot occur when volume/capacity ratios above 0.60 are experienced at peak times on the critical intersection approaches.
Evaluation Precision
25. Quantification of the consequences of the resulting set of public transport line volumes, link flows and turning volumes requires absolute and precise estimation of real not perceived values of the performance measures. The scale of delays and travel times must be properly established:
the value of vehicle occupants’ time varies as differing proportions of working vs non-working vehicle occupants occur in the traffic stream;
temporal variations in approach volumes, and conflicting flows require to be considered to estimate accurate real intersection delays and hence travel times;
6 | P a g e 023 an estimate of the travel costs of users over an entire 25 year period requires delays and travel times to be estimated for a number of representative analysis periods and summed to represent a day; then factored to a year etc.
26. Evaluation then requires the selection of a representative set of analysis periods within which costs are constant and volumes can be reasonably assumed to remain static. Increasing levels of precision imply shorter analysis time intervals.
27. While traditional, particularly strategic level, transportation models have adopted a time period of twenty-four hours; much shorter time periods are essential for realistic evaluation and level of service estimation. Broadly, level 1 analyses would be conducted over time periods between 60 and 120 minutes in duration, level 2 would be 60 minutes, with implicit consideration of shorter time periods down to 15 minutes for level 3 precision. In the latter case the average delay over a 60 minute interval is calculated for each of the short period time intervals which make it up. Whereas level 2 precision would adopt a single uniform flow throughout the entire 60 minutes of the analysis period.
Parking Facility Representation
28. Street network transportation models are concerned with the movement of vehicles between the traffic zones. It is often assumed that adequate parking would be available at each and every activity so that the centroid of parking availability is identical to that of the activities. While this assumption is adequate for residential zones and much low density industrial uses, it is certainly not the case in high- density activity areas such as central business districts.
29. In such locations, parking facilities may be remote from the activity centroid and may even occur in a nearby zone. In such cases special zones in the network representation should represent parking facilities. Alternatively, the trip matrix should be amended to reflect parking availability at the appropriate centroids. In some cases it might be adequate to adjust zone boundaries so as to ensure the parking supply and demand are in rough equilibrium.
30. If and when the parking facilities are directly represented in the network model the number of parking spaces available within the zones should be related consistently to general level of activities per zone taking into account likely parking turnovers per space. Consequently level 3 network representations would represent all
7 | P a g e 024 parking facilities exceeding 50 in number, and level 2, facilities exceeding 100 at the one location.
Recommended Guidelines
31. In summary, transport models should display a consistent and increasing level of precision depending on the accuracy needs of the output. As a broad guide, the general requirements of network and activity level model representation are summarised in Table 1 below.
Table 1: Transport Model Parameters PRECISION LEVEL PARAMETER 1 2 3 Intersection Delays Estimated Links or Turns by Approaches at: Nodes Lane Activity per Zone 1,000 400 250 Centroid Connectors per Zone 4 2 - 3 1 - 2 Analysis Time Period (mins) 60 - 120 15 - 60 10 - 15 Links per Zone 8 5 3 Parking Facilities Directly None or >100 >50 Represented >150 Approx. Peak Direction Flow 1,000 vph 400 vph 250 vph per zone Approx. Accuracy Link Flows 25% 20% 17% (RMS) Approx Precision 250 vph 100 vph 50 vph
32. The final row of the table indicates estimated accuracy levels in terms of vehicles per hour for each of the three precision levels. The tabulated values have been calculated from the previous 2 rows of the table on the assumptions that:
peak hour directional flow rates to or from each zone are approximately equivalent to the activity level;
calibrated models will display Route Mean Square (RMS) errors as indicated;
estimated accuracy then is simply the product of the error times the average peak directional flow rate per zone.
8 | P a g e 025 33. It should be noted that the quoted guidelines are indicative. Variations from the suggested values can and should occur in particular cases. The estimated accuracy levels assume skilful application of transport analysis techniques, properly specified models in other respects, and quote average results throughout the network on the major arterial links.
NZTA Economic Evaluation Manual (EEM) Guidelines
34. In contrast the EEM considers only a single set of validation criteria and recommends that modelled link volumes be predicted with an accuracy of 30% generally and within 20% in the vicinity of the scheme when directly compared with actual measured flows. The manual suggests that the GEH statistic as the main criterion for determining necessary accuracy, requiring 95% to display values less than 4 and 60% less than 5.
Strategic and Project Model Forms
35. The EEM makes a valid distinction between strategic models that involve representation and study of entire metropolitan areas, broad land-use/transport interactions and directly consider the relevant competing modes of travel; with "project models" that involve only a portion of the network for only a single mode. In other words, area wide 3-stage model forms with 1-stage formulations. Quite separate and different evaluation procedures are specified for road network improvement projects as distinct from those involving public transport investments.
36. The Manual mandates the use of Project Models of greater precision than that usually adopted within strategic representations such as those currently available within the major metropolitan areas. Then rather paradoxically, adopts validation criteria levels usually required of well-conditioned strategic studies. Many area wide strategic level studies involve zone sizes having activity levels of about 1,000 equivalent households which are readily capable of predicting arterial link volumes to within 30% of actual counts. The greater precision level of 20% accuracy required near the project receives much lesser emphasis.
Project Evaluations
37. Apparently Project Models are needed to overcome a perceived defect of the strategic models that depended on approximate link based supply functions alone
9 | P a g e 026 for determining benefits. Direct estimation of intersection delays is clearly required. Since reasonably accurate estimates of intersection turning flows are then essential, an improved level of precision must be achieved.
38. The Manual assumes that in most cases the Project Model will itself depend on the strategic model estimates of demand. Greater network detail and the more loading points provided by smaller zones is assumed will ensure that the necessary added precision will be achieved. But the accuracy of the demand estimate will still be that determined by the precision of the strategic model link supply functions.
Validation Criteria
39. The EEM adopts the GEH as the prime criterion for acceptance of model accuracy. This parameter has been selected because it is deliberately biased towards the higher values being compared. Apparently, it is accepted that the lower volumes are less important than the higher values as would be appropriate if the outputs are targeted at design type issues and derived from the link based supply functions common in regional strategic level model forms.
40. Neither the parameter nor the recommended acceptance levels are appropriate when the model is aimed mainly at evaluation issues. The relevant measure of effectiveness is intersection delays that occur along the arterial links where relatively small volumes from the side roads critically determine arterial performance.
41. Either the coefficient of correlation or the root mean square error are then more appropriate. The RMS is preferred as providing a more familiar and direct measure of likely accuracy.
42. The 3 precision levels discussed above would then provide the basis of acceptance criteria thus:
Level 1 - Strategic Level Model Forms;
Level 2 - Corridor Models targeted at evaluation issues;
Level 3 - Local area models aimed at environmental effects.
43. In summary, it is recommended that the following criteria should be achieved for transport models targeted at economic evaluations and broad based consideration of environmental effects:
10 | P a g e 027 Root Mean Square Error: Less than 20 - 25%;
Coefficient of Correlation: Greater than 0.925 – 0.975;
Slope of Regression Line: In the range 0.95 – 1.05.
Alternate Transport Model
44. An alternate transport model has been prepared to provide a sound rational basis to check several aspects of the model form adopted by the applicant, and to aid the design and evaluation of the Enhanced Rotary option developed by Richard Reid. The model form briefly described below is essentially an updated version of the model I used to scheme the Inner City Bypass (ICB) proposal for Transit NZ in the 90’s.
45. The model has been updated to a base year of 2011 using information derived from the WTSM regional model outputs for 2011, NZTA traffic monitoring system (TMS), and details of the directly observed crossings of the W4 regional screen line count data. Turning counts of 2009 detailed in the applicant’s documents have been used to validate the model.
Network Form
46. The alternate model network extends southward from Ngauranga Gorge to encompass the Wellington City CBD and environs within the Town Belt. The boundaries of the model have been deliberately arranged to coincide with the bottlenecks of Ngauranga Gorge (A), the Petone on-ramp merge onto SH 2 (B), and the Mount Victoria Tunnel (C). Only the bottleneck at the Terrace Tunnel (D) lies within the model confines. Most of the relevant bottlenecks then lie on the boundaries to the model where external manipulation can be readily achieved.
47. The southern and eastern boundary also conveniently coincides with the CBD screen line adopted by the WTSM model, enabling ready interaction with the regional model outputs. While Majoribanks, Elizabeth, and Pirie Streets are internal zones in the alternate model; the major arterials crossing the boundary at Oriental Parade, Mount Victoria Tunnel, Adelaide Road, Taranaki Street, and Upper Willis Street are common to both the model and the regional model screen line.
48. The resulting network is illustrated in Figure 1 below, where the 122 internal zones have been hand annotated with small closed circles, and the external zones by
11 | P a g e 028 larger open circles. The bottlenecks are depicted with star shapes and named A,B,C, and D according to the above list. The Lambton Harbour edge has also been added to the computer plot which forms the base of the figure.
49. The figure identifies that the network has been modelled using the software platform TMODEL2 produced by the TMODEL2 Corporation of Seattle, Washington State, USA. I obtained a copy from Robert Schull the proprietor in the 90’s on the understanding I would act as a “proving shop”. I have used this platform for nearly all my recent transport model applications because of its elegant simplicity, ready intervention, and full compatible with procedures I have personally developed.
Figure 1: Alternate Transport Model Network
50. The effects of the internally located bottleneck (D) is replicated in the alternate model by means of a set of pseudo additional links which connect the bottleneck to the likely destinations of the trips held back by the bottleneck (Figure 2 below). In
12 | P a g e 029 effect, an “underground” additional network has been added. This device provides a path for the excess demands over and above that allowed by the capacity limit to be assigned using the normal assignment procedures. Such trips occur on the normal links upstream of the bottleneck, but do not appear on the normal links downstream. The underground portion of the network then contains details of the suppressed demands as to desired destination.
Figure 2: Alternate Network Underground Links and Area 3
51. The underground network links in Figure 2 are coloured green and are shown to connect the bottleneck to destinations reached conveniently from the Terrace Tunnel. Immediately downstream of the point where the underground link connects to the motorway lane representation, a capacity limit is imposed. Such network configurations have been adopted for all network options and analysis periods that apply before duplication of the tunnel.
52. Figure 2 also shows by identifying in red the links included in that portion of the network defined as ‘Area 3”, used for the BCR evaluation described in David
13 | P a g e 030 Young’s evidence. The travel statistics of total vehicle kilometres and vehicle hours used in the evaluations have been limited to the aggregation of Area 3 links.
Model Validation
53. The model has been validated against the link volumes for each period as recorded by the 2009 counts detailed in the applicant’s modelling documentation. It was found that the counts located along most of the relevant arterials in the vicinity of the Basin Reserve are reasonably consistent but that the counts are often inconsistent with the TMS (NZTAs Traffic Monitoring System) machine counts. Some of the calculated RMS (route mean square) error values are thereby inflated.
AM Peak Comparison
y = 1.0243x R² = 0.9633 Model
Count
Figure 3: AM Peak Period Model versus Counts Scattergram
54. The trend line analysis results shown in Figure 3 of 0.96 for the correlation coefficient and 1.02 for the slope of the regression line are well within acceptable values. Figures 4 and 5 below establish that the inter peak (IP) validation statistics also lie within the acceptable range.
14 | P a g e 031 Inter Peak Comparison l y = 1.0537x R² = 0.9324 Mode
Count
Figure 4: Inter Peak Period Model versus Count Scattergram
PM Peak Comparison
y = 1.011x R² = 0.9254 Model
Count
Figure 5: PM Peak Model versus Count Scattergram
55. The crucially important PM peak comparison in Figure 5 displays an RMS error of 25%, and a correlation coefficient of 0.925 which are on the limits of acceptability.
15 | P a g e 032 56. Nevertheless, it is considered that the alternate model is well within the acceptable range for indicative rather than definitive analysis applications.
Demand Forecasting
57. Future demands have been estimated by expanding the base year trip matrices using the FRATAR method. The expansion factors have been derived from the growth ratios recorded on the Wellington City Regional screen lines as described in the GWRC Report TR 19. The alternate model has thereby adopted precisely the same assumptions relating to vehicle traffic growth as the SATURN Model of the Applicant.
58. The same expansion factors have been adopted for each and every zone in the following 5 groups. Group 1: Wellington City CBD and inner suburbs within the WTSM screen line. Group 2: Outer suburbs of Karori, Wadestown and Khandallah etc. Group 3: SH 1 and SH 2 external zones north of the Ngauranga merge. Group 4: Northern and Western inner suburbs. Group5: South Eastern CBD cordon including lower Brooklyn, Taranaki St, Adelaide Rd, Mt Victoria Tunnel and Oriental Parade.
59. The adopted expansion factors for these 5 Groups are illustrated in Table 2 below for the AM Peak period .
Table 2: Expansion Factors Groups 1 to 5 – AM Peak
AM Peak 2021 2021 2031 2031 2041 2041 Out In Out In Out In
Group 1 1.123 1.064 1.218 1.198 1.349 1.273
Group 2 1.071 1.089 1.190 1.151 1.232 1.215
Group 3 1.005 1.102 1.274 1.094 1.146 1.289
Group 4 1.071 1.089 1.190 1.151 1.232 1.215
Group 5 1.008 1.142 1.239 1.314 1.297 1.376
60. Where appropriate, the resulting trip matrix has been further modified to include the estimated effects of the externally located bottlenecks for the year 2021 by limiting them to the measured capacity limit. Following tunnel duplication in the
16 | P a g e 033 years 2031 and 2041, a further FRATAR expansion has been applied to include an assessed revised demand likely to result when the capacity limits are relaxed. It is emphasised that this assessment is essentially an informed guess.
SATURN and TMODEL Outputs Compared
61. Tables 3 and 4 below detail a comparison of the link flows at critical locations as predicted by the alternate (TMODEL) model with that of the SATURN (SATURN) model adopted by the applicant. In each case the results, identified by the cardinal direction of flow (rounded to the nearest 50), are tabulated for both the “Do Minimum” (Domin) and “Proposal” (Bridge) conditions. Table 3 details the situation before the tunnels are duplicated for the analysis year 2021. Table 4 in contrast, details the situation predicted following the duplication of both the Mount Victoria and Terrace tunnels.
62. In general the predictions though similar, differ in some critical aspects. Firstly, the predicted flows northbound in the Terrace Tunnel differ considerably. Secondly, SATURN predicts that construction of the Bridge will cause a diversion of a significant volume of traffic to Adelaide Road.
63. The difference in the results relating to the Terrace Tunnel is largely due to a fundamental difference between SATURN and TMODEL relating to the definition of the AM Peak. SATURN adopts the fixed clock hour of 8:00am to 9:00am universally over the network. Whereas the definition of the peak hour in TMODEL is the maximum sum of any 4 consecutive 15 minute tally intervals whatever the time. The TMS count northbound in the tunnel in 2012 recorded 1640 vehicles between 8:00am and 9:00am, but a peak 4 consecutive 15 minute tally of 1900 between 7:15am and 8:15am.
64. The SATURN prediction that Adelaide Road will experience a sudden substantial increase in demand following opening of the proposal appears to be caused by an assessed significant reduction in travel time from Newtown down Adelaide Road, through the Basin Reserve roundabout to Cambridge Terrace. It appears that the model is allowing free and unfettered access to the Basin at the intersection of Adelaide Road with Rugby Street. I am firmly of the view that the intersection as proposed has been inappropriately modelled. In my view the delays likely to be experienced here will not be significantly less with or without the bridge. The potential conflict between the flows proceeding round the Basin on Rugby Street
17 | P a g e 034 bound for Sussex Street or straight ahead towards Tasman Street with those turning left from Adelaide Road must be controlled with a traffic signal. In addition, the stated intention to provide only 1 lane in each direction for general vehicular traffic the entire length of Adelaide Road would tend to constrain increases here.
Table 3: Estimated Link Volumes SATURN and TMODEL BEFORE Duplication
2021 AM Peak Domin Domin Bridge Bridge
Location Dir SATURN TMODEL Diff SATURN TMODEL Diff
Terrace SBND 1550 1650 6% 1550 1650 6%
Tunnel NBND 1900 2300 21% 1900 2350 24%
Mt. Victoria WBND 1550 1600 3% 1600 1600 0%
Tunnel EBND 1400 1200 -14% 1400 1250 -11%
Adelaide Road NBND 1250 1000 -20% 1400 1000 -11%
SBND 650 600 -8% 1050 600 -43%
Kent Terrace SBND 2200 1950 -11% 2550 1950 -24%
Cambridge Tce NBND 900 750 -17% 800 500 -38%
Oriental WBND 1500 1100 -33% 1450 1100 -18%
Parade EBND 850 750 -12% 850 750 -12%
65. The situation after duplication described in the second table below with a similar layout reveals much greater differences in predicted link flows at the critical locations. By far the greatest difference relates to the estimates of likely flows through the relieved bottlenecks at the duplicated tunnels. However, the potential differences are somewhat obscured by the need to limit the assessed demands westbound through the Mount Victoria Tunnel to match the capacity of the planned improvements at the eastern approaches to the tunnel. The westbound demand estimated for the Mount Victoria Tunnel has been set to the low value of the likely range in TMODEL to comply with the limited capacity of the eastern approach roadways of Wellington Road and Ruahine Street. It is assumed that the proposed
18 | P a g e 035 Wellington/Ruahine intersection will be limited to 2 through lanes and be provided with a green display of about a 60% of the cycle time.
Table 4: Estimated Link Volumes SATURN and TMODEL AFTER Duplication
2031 AM Peak Domin Domin Bridge Bridge
Location Dir SATURN TMODEL Diff SATURN TMODEL Diff
Terrace SBND 2300 35000 52% 2300 35000 52%
Tunnel NBND 2200 2800 29% 2300 2900 26%
Mt. Victoria WBND 1750 2250 29% 2300 2250 -2%
Tunnel EBND 2000 1600 -20% 2100 1600 -24%
Adelaide Road NBND 1250 1150 -8% 1400 1150 -18%
SBND 650 800 23% 950 800 -16%
Kent Terrace SBND 2750 2550 -7% 3150 2550 -18%
Cambridge Tce NBND 990 1200 21% 1050 600 -45%
Oriental WBND 1500 1100 -33% 1200 1000 -17%
Parade EBND 500 800 60% 500 800 50%
Traffic Signals analysis using INTPER32
Analysis Procedure
66. The technique adopted for my analysis follows the ideas developed by Wooton Jeffries Associates for the UK Department of Transport, later incorporated into the Cost Benefit Analysis suite of procedures. Essentially, all approaches to any type of intersection are reduced to a queuing condition represented by only two variables,
2 Intersection Performance sub-model abbreviation.
19 | P a g e 036 the “capacity” and a queuing parameter. In general, a queue is considered for each lane on all approaches separately: The “capacity” is the reciprocal of the average service time as defined in the Queuing Theory. It represents the maximum flow rate possible, or the flow through the approach while a queue is permanently present. The queue parameter has a value of :
1.00 - random arrivals, random service time distributions;
0.55 - at traffic signals where service times are more uniform etc.
67. This device allows the queue lengths and therefore the delays due to queuing to be calculated in a consistent (the same) manner whatever the intersection type. In effect, the delay calculation is indifferent to the intersection type.
68. Finite delays are assessed for the “over-saturated” case by an approximation to the likely delay function (by transformation) in the manner suggested by Kimber and Hollis of the Transport and Road Research Laboratory3 using dynamic queuing considerations. The procedure INTPER3 adopts exactly these latter procedures and computer algorithm.
69. Generally, the queue capacity calculations follow Australian Road Research Board procedures commonly used in New Zealand., rather than the USA methods prescribed in their Highway Capacity Manual. The method of dynamic queues allows the calculation of finite delays when capacity is exceeded over a short time interval during the flow period analysed.
Traffic Signal Operation
70. The programme assumes the signal controller is provided with a detection system that ensures sufficient green will be guaranteed to clear any queue present at the onset of green plus vehicles which may join during the time necessary for the queue to clear. The programme estimates the necessary minimum green according to the usual formulae. If the input minimum green setting is larger, the phase time is fixed accordingly.
3 Refer TRRL Laboratory Report 909 (1979), Departments of Environment and Transport, UK,
20 | P a g e 037 71. After the minimum green time, a green extension period is calculated. It is assumed that a gap between successive detections is being sought equal to the vehicle extension interval. In the present version, the vehicle extension interval is calculated internally, rather than input as an externally determined controller setting. The vehicle extension algorithm roughly simulates a “density” controller where the vehicle extension reduces with time. If a pre-set maximum green setting is exceeded, the maximum green input value determines the total green interval.
72. An iterative technique is adopted to find stable green, and therefore cycle times. The queues produced by the input minimum green settings start the process. Stability is determined by the criterion that a revised cycle time less than two seconds different from the previous value will terminate the iterations.
73. Phase times and therefore cycle times will be determined by the maximum green settings when saturation ratios rise above about 75%. The performance of the installation is then very sensitive to the input settings.
Temporal Demand Variations at Traffic Signals
74. The effect of temporal variations in demand over an extended analysis period is calculated within the programme using approach specific demand profiles. This data set specifies the ratio of actual demand expected in each time increment as a percent of the average flow rate implied by the trip table being assigned. Thus during the crest of the AM peak say, a value of 115% may apply for the intense 15 minute interval preceded by values of 85, 95, 105 for example, when the trip table contains the average flow rate during a 60 minute period. Obviously, the sum of the four profile incremental values over this time period must total 100%.
75. The real world variations in demand that occur can then be reasonably replicated. The peak intensity on any approach will often be displaced from that of the other approaches etc. In this application a standard profile derived from short period directional counts would apply for the peak direction of travel, the reverse peak direction on the major arterials, with a third general profile applying to the minor cross streets.
76. The procedure then readily allows the range of a single assignment to be extended into the shoulder periods located either side of the peak. In this case 14 incremental profile values of 15 minutes duration are adopted to represent an entire PM period
21 | P a g e 038 extending over the 3.5 hours from 3:30 pm to 7:00 pm. The range of applicability of the one hour assignment representing the demands between say 4:45 pm to 5:45 pm is then conveniently extended. The consequential 15 minute by 15 minute variations in delay are then available for evaluation purposes without the need to divide the overall PM period into separate "time-slices".
Delay Estimates at Traffic Signals
77. Delay estimates are calculated for each elemental time increment of the flow profile. Separate calculations are undertaken for the “uniform” and “overflow” delay components associated with traffic signals. The ARR 123 formula for uniform delay is adopted. This result is factored by an efficiency factor according to the method specified in the EEM. The efficiency factors are either assumed to be 0.85 (standard for V/A controller) or as input in the movement records.
78. The “overflow” delay component is calculated using the dynamic queuing procedure due to Kimber and Hollis of TRRL Report 909 (refer note 3 above). The suggested delay function transformation and algorithm are incorporated without amendment. The resulting estimate of the overflow delay component is thus more accurate than the conventional analysis method because the actual shape of the demand profile is integrated increment by increment. Further, any overflow queue present at the end of each incremental time interval becomes the initial queue for the next increment. The effect of the dynamic build up and decay of the overflow queue is directly estimated.
Delays at the Basin Reserve Traffic Signals
Before Duplication
79. Figure 6 below illustrates the calculated delay (as a solid black line) experienced on a 2 lane approach to a 2 phase traffic signal having a cycle time of 90 seconds and a phase split of 50/50 according to the delay formulae of Australian Road Research Report (ARR) 123. The plotted points and joining red line are derived from successive runs of INTPER3 for differing approach flow rates. The cycle time and phase splits are then consistent with the measured values at the Patterson Street/Dufferin intersection recorded in Appendix D of the CBD Paramics Modelling Validation Report included in the Application documents. The saturation
22 | P a g e 039 flow rate adopted of 1800 veh/hour of green per lane is consistent with measurements I made recently.
300
250
200
150
100 Calculated Delay (Secs/Veh)
50
0 500 1000 1500 2000 2500 SH 1 Volume ex Mt. Victoria Tunnel
Figure 6: Approach Delays at the Patterson Street traffic Signal
80. As is common for all traffic signal installations the relationship between approach flow rates and delays is a function that suddenly steepens near the capacity of the approach. In this case, a value of about 1900 veh/hr. Delays when approach flows are less than 1600 veh/hr vary only slightly in the range of 20-30 seconds per vehicle.
81. The delay formulae of ARR 123 assumes that during the entire analysis period of 60 minutes the approach flow rate remains fixed at the input value and that the cycle time and phase splits are also constant. Real world flows however vary with time and real world traffic signal controllers vary the cycle time and phase splits in response to such changing inputs. The analysis in Figure 7(a) below is derived from INTPER3. It shows the effects of such real world responses at this site.
82. Figure 7(a) shows by means of a bar graph the flows emerging from the tunnel in Patterson Street, together with the cycle time (red line) and delays (green line)
23 | P a g e 040 experienced on that approach to the signal. Both these variables are referenced by the right hand vertical axis depicted in the diagram.
1800 140
1600 120 1400 100 1200
1000 80
800 60
600 40 400 Cycle Time andDelay (secs) Patterson St Flow (veh/hr)Rate 20 200
0 0 7:00 7:30 8:00 8:30 9:00 9:30 10:00
Figure 7(a): Patterson Street Approach to Basin Reserve Signal
83. Since the flows emerging from the tunnel downstream of the bottleneck are constant over the period from 7:45 am to 9:15 am, the cycle time and therefore delays vary due to the changing demands on the other approach. During the peak 60 minutes from 8:00am to 9:00am the cycle time averages 95 seconds and the delays average slightly less the 30 seconds per vehicle. These values are entirely consistent with the calculation described above.
84. However, the flows on the Dufferin Street approach to the same signal (intersection with Patterson St), shown in Figure 7(b) below, vary significantly rising rapidly from a low value prior to 7:00am to a peak at about 8:00am, then decline to a moderate steady value after 9:00am. Consequently the cycle time and phase splits alter; resulting in an average delay on this approach of slightly in excess of 30 seconds per vehicle, or an LOS near the usually accepted satisfactory level of C.
24 | P a g e 041 1800 140
1600 120 1400 100 1200
1000 80
800 60
600
40 Cycle Time andDelay (secs) Dufferin St Flow Rate (veh/hr) 400 20 200
0 0 7:00 7:30 8:00 8:30 9:00 9:30 10:00
Figure 7(b): Dufferin Street Approach to Basin Reserve Signal
85. Consequently the capacity limit imposed by the Mount Victoria Tunnel effectively precludes the Paterson/Dufferin Street intersection suffering a significant deterioration in level of service while the tunnel remains a 2-lane 2-way facility.
Intersection Delays Before and After Duplication Compared
86. The intersections located along the one-way pair of SH 1 have been analysed by INTPER3 using the turning volumes predicted by the TMODEL transport model for the two flow regimes of before and after the tunnels are duplicated. The results are tabulated below for the AM and PM peaks of the nominal analysis years of 2021 and 2031. The table details the estimated average delay for the intersection as a whole in units of seconds per vehicle and identifies the corresponding Level of Service (LOS) according to the USA Highway Capacity Manual criteria.
25 | P a g e 042 Table 5:SH 1 Westbound Average Intersection Delays (secs/vehicle) and LOS
Intersection 2021 LOS 2021 LOS 2031 LOS 2031 LOS AM PM AM PM
Dufferin St 30 C 30 C 15 B 12 B
Adelaide Rd 15 B 17 C 21 C 18 C
Taranaki St 24 B 24 C 27 C 24 C
Cuba Street 12 B 13 B 13 B 13 B
Victoria St 16 C 21 C 17 C 28 C
Willis Street 19 C 15 B 22 C 14 C
87. The table headings have adopted the convention introduced by the NZTA documents that year 2021 denotes the conditions before duplication, and year 2031 after. It is assumed that the network analysed for year 2021 retains the present layout round the Basin Reserve and incorporates the ICB improvements along the route beyond Taranaki Street. However, unlike the Opus SATURN analysis, I have assumed the widened facility having 3 through lanes beneath the Memorial Park structure will be available since they are being constructed as part of the current Buckle Street Project.
88. The network adopted for conditions after duplication envisages an enhanced Basin Reserve roundabout having 3 through lanes along Patterson Street and thence round the Basin Reserve to Buckle Street. In effect, the same design standard that applies throughout the rest of the route.
89. The analysis clearly shows that an at-grade westbound SH 1 route having 3 through lanes consistently along the route operates with a satisfactory level of service both before and after duplication of the tunnels. There will be no congestion experienced westbound on typical weekdays. But it must be emphasised that this conclusion critically depends on the supplied capacity on the eastern approaches to the Mount Victoria Tunnel.
26 | P a g e 043 90. In severe contrast, the SH 1 eastbound route along Vivian Street will suffer a severe deterioration in level of service after duplication of the Terrace Tunnel as detailed in the Table 6 below.
Table 6: SH 1 Eastbound Average Intersection Delays (secs/vehicle) and LOS
Intersection 2021 LOS 2021 LOS 2031 LOS 2031 LOS AM PM AM PM
Willis St 15 B 16 C 154 F 44 D
Victoria St 14 B 21 C 29 C 55 E
Cuba St 17 B 17 C 26 C 47 D
Taranaki St 26 C 39 D 70 E 230 F
Tory St 12 B 13 B 15 B 20 C
Cambridge 19 C 21 C 24 C 27 C Tce.
91. Once again, the results for the after duplication condition depend critically on details of the distant upstream situation that will apply following duplication. The precise layout of a widened SH 1 south of the Ngauranga Interchange, the design of the lane-drop at the Aotea Off-Ramp, and the exact layout of the motorway south of the structure over Bowen Street is unknown. The estimates of likely flows issuing from a duplicated Terrace Tunnel amounts to no more than an informed guess. But there is no doubt there will be sufficient pent-up demand to overwhelm the somewhat limited facility improvements that have been indicated by NZTA so far. There will still be bottlenecks north of Wellington City in addition to the untreated conditions on SH 2 between Petone and Ngauranga after completion of the RONS proposals.
92. The analysis emphatically confirms the conclusion reached by application of the TMODEL model form when applied during the scheming of the ICB that the critical intersection along both the SH 1 routes involves Taranaki Street. In comparison the Basin Reserve roundabout in its present form is only a minor impediment to travel along either route.
27 | P a g e 044 93. A cogent case for a substantial increase in capacity over this section of the westbound route is not indicated by consideration of the utilisation ratio and surplus capacity indicators. The INTPER3 analysis provides details enabling the utilisation ratio to be determined for each intersection (refer Table 7 below). The ratio is simply defined as the total volume of traffic entering the intersection divided by the entering volume that will result in a satisfactory level of service in the C-D range. While the ratio is less than 1.00 the intersection achieves its proper function.
Table 7: SH 1 Westbound Intersection Utilisation Ratios
Intersection 2021 AM 2021 PM 2031 AM 2031 PM
Dufferin Street 0.91 0.91 0.74 0.71
Adelaide Road 0.75 0.78 0.83 0.79
Taranaki Street 0.86 0.86 0.72 0.85
Cuba Street 0.70 0.71 0.78 0.72
Victoria Street 0.76 0.82 0.84 0.90
Willis Street 0.80 0.74 0.86 0.80
94. While the Dufferin Street and Adelaide Road intersections in their present form are adequate in the 2021 situation (noting the 2021 situation assumes the status quo rotary); the enhanced Basin Reserve roundabout option performs well in the 2031 condition. The enhancement could be readily implemented prior to the tunnels being duplicated, and the utilisation ratios analysis in Table 7 above indicate that should at least be considered.
95. In contrast to the eastbound route, Table 8 below shows the eastbound SH 1 route has insufficient capacity to cope with the expected demands delivered by a duplicated Terrace Tunnel. In spite of the ICB improvements that provide 3 through lanes throughout the route, the intersections at Willis Street and particularly Taranaki Street are severely overloaded following duplication of the Terrace tunnel.
28 | P a g e 045 Table 8: SH 1 Eastbound Intersection Utilisation Ratios
Intersection 2021 AM 2021 PM 2031 AM 2031 PM
Willis Street 0.76 0.76 1.40 1.01
Victoria Street 0.74 0.83 0.90 1.07
Cuba Street 0.78 0.78 0.88 1.03
Taranaki Street 0.88 0.98 1.14 1.54
Tory Street 0.71 0.72 0.74 0.81
Cambridge Tce 0.80 0.82 0.85 0.89
96. NETSIM is a long standing micro-simulation model developed in the USA in the 1950’s to aid the optimum setting of a dense set of traffic signals controlling the grid street layout of a typical urban area. The software package has been the state-of- the-art analysis system since the late 1970’s. I have applied an earlier version many times during my career at Roading Division of the Ministry of Works and later at Traffic Design Group here in Wellington. I used this model for the Mana Esplanade Improvement Project. That involved studying the operation of the 5 sets of linked signals along SH 1, with and without the presence of a High Occupancy Vehicle (HOV) lane. The developed design was built.
97. I have analysed the operation of the Basin Reserve roundabout from the Mount Victoria tunnel western portal to Buckle Street using the same NETSIM model for 3 cases. Two cases consisting of the present layout loaded with the Opus traffic flows detailed in the SATURN model outputs for both the base year and future 2021 conditions during the AM, IP and PM periods. The third case being a 3-lane circulating layout similar to the Enhanced Roundabout Option subject to the Opus derived 2031 AM, IP (interpeak), and PM period conditions. The results are tabulated in Appendix 1 attached.
98. Appendix 1 provides a comprehensive set of results of a 15 minute period where the flows are held constant. NETSIM predicts unequal lane usage at the Dufferin Street stop line with Paterson Street. This is consistent with real world observations. The top section of the table shows the total travel time round the Basin along the SH 1 route from Paterson Street to a point in Buckle Street at the previous position of the
29 | P a g e 046 Tory/Tasman Street intersection. The penultimate row contains the rounded total travel time in seconds. It is clear that there is virtually no difference between the 2021 situation than that of the base year of 2009. This result confirms my contention that the S-Paramics model result that there is a huge increase in travel time is erroneous. There can then be no benefit in constructing the proposed bridge.
99. The middle tables of Appendix 1 also confirm very small differences in the travel times on the cross road routes Kent Tce to Adelaide Rd, and Adelaide Rd to Cambridge Tce. The result for the northbound route in the 2021 AM peak is an aberration caused by the Opus SATURN model calibration error for Adelaide Road demands passed to the S-Paramics model via the cordon defined trip matrix transfer.
100. The final sector of the table in Appendix 1 shows the performance of the pair of traffic signal controlled intersections at the Basin. It is clear that an acceptable level of service as defined by the USA Highway Capacity Manual can be expected at both intersections in the flow regime prior to the tunnel duplications.
101. The “future layout” columns in Appendix 1 show preliminary results for the Basin Reserve Enhancements Option that is based on 3 circulating lanes. The analysis shows that the design can handle the huge increase in flows I have estimated will occur in the flow regime following duplication of the Terrace and Mt Victoria Tunnels. It should be noted that this preliminary design is still being refined and will be described in detail in Mr Richard Reid’s evidence.
Intersection Delays After Duplication Compared
102. Table 9 below provides a comparison of the Basin Reserve Enhancements Option with that of the Basin Bridge Option following duplication of the Mount Victoria tunnel. The signal cycle times, phase splits and consequential delays have been derived from the computer program INTPER3 analysis of the outputs from the TMODEL alternate model formulation. The first table details the estimated approach delays and average intersection delay in units of second per vehicle.
30 | P a g e 047 Table 9: Estimated Vehicular Traffic Delays for Year 2031 After Duplications
Secs/veh Enhanced Roundabout Option Bridge Option
Approach 2031 AM 2031 IP 2031PM 2031 AM 2031 IP 2031 PM
Paterson 13 11 12 34 19 29
Dufferin 18 10 13 27 22 26
Average: 14 11 12 28 21 29
Rugby 21 13 17 15 11 16
Adelaide 25 14 18 41 19 40
Average: 21 14 19 52 19 95
103. It should be noted that the average intersection delays for the Rugby/Adelaide intersection includes delays to traffic turning left from Rugby Street to Adelaide Road. The NZTA design has been modelled as if pedestrian demands are satisfied on all cycles. The single lane provided for these left turners then has insufficient capacity to provide a satisfactory level of service.
104. It is apparent that the Enhanced Roundabout Option performs well providing a Level of Service in the range B-C in all cases. The Bridge Option, on the other hand, while also providing a satisfactory Level of Service to the Rugby Street and Adelaide Road approaches, has higher vehicular delays in all cases.
105. Table 10 below details estimated delays in seconds per vehicle incurred by buses travelling up and down Adelaide Road from either Kent or Cambridge terraces. Delays have been estimated by assuming buses will be given preference by always being first to receive green at the head of any queue stopped by a red signal. A delay equal to the uniform delay will then be experienced. In this case, only two approaches are involved.
31 | P a g e 048 Table 10: Estimated Delays for Buses in Year 2031 After Duplication
Secs/bus Enhanced Roundabout Option Bridge Option
Approach 2031 AM 2031 IP 2031 PM 2031 AM 2031 IP 2031 PM
Dufferin 14 13 10 8 8 8
Adelaide 16 12 11 24 9 24
106. Table 10 shows that the Bridge Option favours southbound buses on the Dufferin Street approach to the Paterson/Dufferin intersection by some 2-6 seconds per vehicle, but delays northbound bus movements by a greater extent on the Adelaide Street approach than the Enhanced Roundabout Option. The single lane provided for the traffic eastbound on Rugby Street together with necessary pedestrian clearance times create inefficiencies at this intersection
107. The delays estimated to be borne by pedestrians are detailed in Table 11 below. They have been calculated as being half the red signal time at the crosswalks located on the named approach. It has been assumed that pedestrian arrivals are uniformly spaced and that every cycle responds to a pedestrian call.
Table 11: Estimated Delays to Pedestrians in Year 2031 After Duplication
Secs/ Enhanced Roundabout Option Bridge Option person
Approach 2031 AM 2031 IP 2031 PM 2031 2031 IP 2031 PM AM
Paterson 22 15 15 32 32 28
Dufferin 25 17 17 16 17 16
Rugby 27 17 15 17 21 33
Adelaide 25 17 17 36 17 35
108. The inherent inefficiencies of the Bridge Option again cause delays to users of the intersections of the Bridge Option to be more than the alternate option. While a few cases favour the Bridge Option layout the general result is that the Enhanced Option is similar or better. The relatively long wait times to cross the left turn out of
32 | P a g e 049 Adelaide Road northbound estimated above would be much larger if the Opus estimate of the volume turning was used in the analysis.
33 | P a g e 050 Appendix 1: NETSIM Analysis for SH1 Westbound
Results NETSIM Analysis Table of Results from NETSIM Models with Weaving on Links 4-1,1-2, and 2-3)
Present Layout Future Layout SH 1 Westbound ( 2 Circulating lanes ) ( 3 Circulating Lanes ) Base Year 2009 Future Year 2021 Future Year 2031 Travel Time (secs) Link AM IP PM AM IP PM AM IP PM Patterson 5-1 81.2 70.2 72.8 80.7 70.2 71.5 96.4 64.3 116 Dufferin+Rugby 1-2 30.6 29 34.9 35.6 26.9 34.6 58 58 66.8 Rugby+Sussex 2-3 36.7 35.5 36.8 36.9 35.1 36 37.2 37.2 37.1 Buckle 3-7 22.1 21.5 22 22.5 21.7 21.7 22.1 22.2 22.8 170.6 156.2 166.5 175.7 153.9 163.8 213.7 181.7 242.7 Rounded Total: 170 155 165 175 155 165 215 185 250 INDEX: 100 100 100 103 100 100 126 119 152 System Statistics Vehicle- Hours Move 22.23 18.24 22.18 24.87 18.37 24.08 32.49 27.12 31.17 Delay 13.17 9.1 13.19 19.23 8.36 14.35 25.52 14.84 29.03 Total: 35.4 27.34 35.37 44.1 26.73 38.43 58.01 41.96 60.2 Rounded Total: 35 27 35 45 25 38 58 42 60 Delay Proportion: 37% 33% 37% 44% 31% 37% 44% 35% 48% Vehicle Kilometres: 1.61 942 777 942 1055 776 1022 1380 1317 1397 System Speed:(kph) 27 28 27 24 29 27 24 31 23 Cross Road Routes: Southbound: Base Year 2009 Future Year 2021 Future Year 2031 Travel Time (secs) Link AM IP PM AM IP PM AM IP PM Kent Terrace 8-4 22.4 22.3 22.5 22.4 22.3 23 22.8 22.8 23.5 Ellis+Dufferin 4-1 47.6 42.4 46.6 46 41.7 44.5 58 58 66.8 Dufferin+Rugby 1-2 30.6 29.8 34.7 35.6 26.9 34.6 39.8 36.2 43.8 Adelaide Road 2-6 43.1 42.5 43.1 43.5 42.5 44 39.6 39.5 38.7 143.7 137 146.9 147.5 133.4 146.1 160.2 156.5 172.8 Rounded Total: 145 135 145 150 135 145 160 157 173
Northbound: Base Year 2009 Future Year 2021 Future Year 2031 Link AM IP PM AM IP PM AM IP PM Adelaide Road 6-2 75 70.2 79.5 119.6 65.1 86.2 81.9 61 81.2 Rugby+Sussex 2-3 36.7 35.5 36.8 36.9 35.1 36 37.1 37.2 37.1 Ellis Street 3-4 16.1 16 16.7 16.1 15.9 16 15.9 15.3 16.5 Cambridge Terrace 4-8 21.2 21.4 21.4 21.3 21.3 21.3 21.1 21.2 21.2 149 143.1 154.4 193.9 137.4 159.5 156 134.7 156 Rounded Total: 150 145 155 195 140 160 156 135 156
Traffic Signal Delays Base Year 2009 Future Year 2021 Future Year 2031 Queue Time (Seconds): AM IP PM AM IP PM AM IP PM Patterson 5-1 44.8 33.9 36.4 44.3 33.9 35.2 96.4 64.1 96.4 Dufferin 4-1 29 23.9 28 27.8 23.1 25.9 58 58 58 Rugby 1-2 11.9 11.1 16.2 16.8 8.2 15.8 39.8 36.2 39.8 Adelaide 6-2 38.6 33.9 43.1 83.3 28.7 49.9 81.9 61 81.9 Stop Time (Seconds): Patterson 5-1 24.5 17.9 18.7 23 18.7 19.7 29.8 13.2 42.1 Dufferin 4-1 23.6 19.1 22.4 22.6 17.7 18.3 27 31.3 38.2 Rugby 1-2 3.4 4.5 6.8 6.7 2.3 6.6 13.2 10.9 14.5 Adelaide 6-2 25.3 23.6 29.1 53.3 19.7 31.5 31.1 15.2 28.1
Base Year 2009 Future Year 2021 Future Year 2031 Levels of Service (HCM (USA)): AM IP PM AM IP PM AM IP PM Patterson 5-1 C C C C C C C B D Dufferin 4-1 C C C C C C C D D Rugby 1-2 A A A B A B B B B Adelaide 6-2 C C C D C C D B C
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