RUNNYMEDE BOROUGH COUNCIL
SAFER RUNNYMEDE SPEED INITIATIVE
INTERIM REPORT FEBRUARY 2003
Document Title: INTERIM REPORT FEBRUARY 2003
Client Reference: SAFER RUNNYMEDE SPEED INITIATIVE
Date: Wednesday, 19 February 2003
Prepared By TRL : M A Winnett, and S A Farmer
Sign ......
Amendment List Iss. / Rev. Iss. / Rev Date Remove Insert Page Iss. / Rev. Page Iss. / Rev. Draft ver 1.0 Tuesday, 10 December 2002 Draft ver 1.5 Thursday, 23 January 2003 Interim ver 1.6 Tuesday, 18 February 2003
CONTENTS
1. INTRODUCTION ...... 1
2. SAFER RUNNYMEDE INITIATIVE...... 2
3. LOOP AND SIGN LOCATIONS...... 2
4. RESULTS...... 4
4.1 Installation information ...... 4 4.2. Effectiveness of the VAS ...... 4 4.3 Summary overview...... 8
5. ACCIDENT BENEFITS ...... 19
6. DISCUSSION...... 22
6.1 General observations ...... 22 6.2 Guildford Road, Ottershaw - Sites 1a and 1b ...... 22 6.3 Chobham Road, Ottershaw - Site 2 ...... 22 6.4 Holloway Hill, Chertsey - Site 3...... 23 6.5 Guildford Road, Chertsey - Site 4 ...... 23 6.6 Chilsey Green Road, Chertsey - Sites 5a and 5b ...... 23 6.7 Chertsey Lane (South), Hythe - Site 6...... 23 6.8 Chertsey Lane (North), Hythe - Site 7...... 24 6.9 Chertsey Lane, Egham Hythe, Northbound...... 24
7. CONCLUSIONS...... 24
8. REFERENCES ...... 25
Appendix A: BACKGROUND TO VEHICLE-ACTIVATED SIGNS (VAS) ...... 26
REFERENCES ...... 33
1. INTRODUCTION
Runnymede Borough Council (Safer Runnymede) have implemented a Speed Initiative under the direction of the Safer Runnymede Manager, Mr David Dodd. The theme of the initiative is "Educate the Majority - Prosecute the Minority".
The longer-term aim is casualty reduction with the more immediate priority of highlighting to the community that action is being taken to address the speeding issue.
The report is structured as follows:
• The rationale behind the Runnymede Initiative • Methodology for monitoring and installation • The results of the Runnymede Initiative • The effectiveness of Vehicle-Activated Signs (VAS) • Reduction in speed • Reduction in percentage of "high end" speeders • Predicted accident benefits • Implications resulting from the trial. • Appendices: • Detailed data • Background to the development of Vehicle-Activated Signs (VAS)
1 2. SAFER RUNNYMEDE INITIATIVE
Re-educating drivers is an on-going campaign throughout the county supported by both Surrey Police and Surrey County Council. Regular Speed Advice Days are held on appropriate routes, when motorists caught speeding are given the choice of three points on their licence or a short lesson on the dangers and consequences of speeding. This includes a test of their driver-awareness and a feed-back questionnaire to provide useful background data for further analysis.
The busy A320 in Runnymede, a main feeder route through the borough, was chosen for an innovative pilot scheme to change driver attitudes to speeding. Many drivers exceed the 30mph and 40mph speed limits along the A320 and its main feeder routes with data showing that as many as 90% of drivers travel above the speed limit. The route also carries high volumes of vehicles, and accident statistics pinpoint it as a route worthy of traffic management.
The 'Safer Runnymede Partnership' consisting of Runnymede Borough Council, Surrey County Council and Surrey Police, and the Transport Research Laboratory developed an initiative to install Vehicle-Activated Signs (VAS. See Appendix A for a functional description of VAS and details of performance) at locations along the route. The initiative was in response to surveys of local people, which have shown fast traffic and motorists who break speed limits to be high on the list of concerns across the county when it comes to law and order issues.
Sited in an urban corridor between Ottershaw in the south and Egham Hythe in the north, the VAS went live at 10am on Wednesday 28 August 2002. The series of VAS light up to reinforce the speed limit if vehicles approach too fast. The message is repeated along the route (Figure 3.1), making it difficult to ignore. The scheme also has the capability to identify persistent offenders.
3. LOOP AND SIGN LOCATIONS
As part of the project evaluation, inductive loops were installed close to the locations where additional measures such as VAS would be installed. Speeds were recorded using these loops before any measures were installed to obtain a speed baseline. Speed recordings were made after the measures were installed to assess what changes had occurred.
Seven bi-directional inductive loops sites were installed in January 2002, (see Figure 3.1) and logging commenced immediately using Counters and Accessories Per Vehicle Record (PVR) data loggers. The locations of the VAS are shown in Figure 3.2. Some additional data were collected from road tubes using MetroCount data loggers.
Loop sites were located over 50 metres downstream from the VAS in order to assess whether the speed reduction was very localised or extended beyond the signs.
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Figure 3.1. Inductive loop monitoring locations
© Crown copyright. All rights reserved. Licence No. AL100021177
Figure 3.2. Location of VAS.
5a 7 5b 30 40
4
3 40 40 6
1b
2 30 40
40
1a
3 The VAS were designed and installed by Westcotec 1.
4. RESULTS
4.1 Installation information
Baseline (BEFORE data) data were collected from inductive loops in January 2002. Post operational data (AFTER data) were collected in October 2002.
The VAS were installed during the summer 2002 after authorisations had been received from the Department for Transport (DfT) and power supplies to the installations were connected in August 2002.
The date of commissioning for the VAS was the 19th August 2002 with the first (southernmost) sign being connected to the mains power supply at 10:37am.
Details of the location and co-ordinates (OSGR) for the VAS and the type of sign are given in Table 4.1
Table 4.1 Details of the VAS locations
Sign Sign location OSGR Sign Loop Direction number type number targetted 1a A320 Guildford Rd Ottershaw TQ 01858-63004 40mph 1 N. b'd jcn Beech Hall (LC146) 1b A320 Guildford Rd Ottershaw TQ 01992-63819 40mph 1 S. b'd adj The Willows (LC139) 2 Chobham Rd Ottershaw TQ 01892-64316 30mph 2 E. b'd opp jcn Flower Crescent 3 B386 Holloway Hill Chertsey TQ 02484-65991 40mph 3 E. b'd o/s Squires Hill Garden Centre 4 A320 Guildford Rd Chertsey TQ 03332-66662 Camera 4 E. b'd adj LC28 5a A320 Chilsey Green Rd Chertsey TQ 03410-67333 Camera 5 N. b'd o/s no 6 opp Frithwald Rd 5b A320 Chilsey Green Rd Chertsey TQ 03282-67547 30mph 5 S. b'd o/s no 41 adj LC4 6 A320 Chertsey Lane jcn Norlands TQ 03672-69558 40mph 6 N. b'd adj LC98 7 A320 Chertsey Lane Hythe TQ 03417-71329 40mph 7 S. b'd o/s no 67 adj LC26
The signs were switched to operate at 10am on Wednesday 28 August 2002.
4.2. Effectiveness of the VAS
The detailed speed and flow data for the Before/After situation is given in a separate document, Annexe A to the Interim Report.
The basic summary statistics are given in Table 4.2.1 and 4.2.2 below.
1 WESTCOTEC Contact: [email protected] www.westcotec.co.uk
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Table 4.2.1. Summary of speed changes (Red indicates a reduction in speed)
5
Table 4.2.1. Summary of speed changes (continued) (Red indicates a reduction in speed)
6
Table 4.2.2. Summary of percentage speed changes (Red indicates a reduction in speed)
7 Table 4.2.2. Summary of percentage speed changes (continued) (Red indicates a reduction in speed)
4.3 Summary overview
A summary sheet for each installation are given below (Sheet 4.3.1 to Sheet 4.3.10)
8 Sheet 4.3.1 Guildford Road, Ottershaw, Northbound
Sign Location: Guildford Rd Ottershaw Speed limit OSGR: TQ 01858-63004 40mph Site Description Urban commuter link
Reason for installation Inappropriate speed for conditions
Installation date 19th August 2002 Activation date 28th August 2002 Sign settings Trigger speed 40mph Sign “on” time 4 seconds Detection distance 100 metres Direction targetted N B'd Monitoring loop location Distance from sign 200 metres beyond sign Effectiveness
Comments: VAS can be seen for at least 300metres. Although south facing, the legend is clearly visible in sunlight.
© Crown copyright. All rights reserved. Licence No. AL100021177
9 Sheet 4.3.2 Guildford Road, Ottershaw, Southbound
Sign Location: Guildford Rd Ottershaw Speed limit OSGR: TQ 01858-63004 40mph Site Description Urban commuter link
Reason for installation Inappropriate speed for conditions
Installation date 19th August 2002 Activation date 28th August 2002 Sign settings Trigger speed 40 mph Sign “on” time 4 seconds Detection distance 100 metres Direction targetted S b'd Monitoring loop location Distance from sign 100 metres beyond sign Effectiveness (Speed change mph)
Comments: Very good contrast with background foliage.
© Crown copyright. All rights reserved. Licence No. AL100021177
10 Sheet 4.3.3 Chobham Road, Ottershaw
Sign Location: Chobham Rd, Ottershaw Speed limit OSGR: TQ 01892-64316 30mph Site Description Urban commuter link
Reason for installation Inappropriate speed for conditions
Installation date 19th August 2002 Activation date 28th August 2002 Sign settings Trigger speed 30 mph Sign “on” time 4 seconds Detection distance 150 metres Direction targetted N b'd Monitoring loop location Distance from sign 100 metres beyond sign Effectiveness
Comments: Hedge needs to be regularly trimmed to avoid obscuration of sign and detector.
© Crown copyright. All rights reserved. Licence No. AL100021177
11 Sheet 4.3.4 Holloway Hill, Chertsey
Sign Location: B386 Holloway Hill Speed limit OSGR: TQ 02484-65991 40mph Site Description Urban commuter link
Reason for installation Inappropriate speed for conditions
Installation date 19th August 2002 Activation date 28th August 2002 Sign settings Trigger speed 40 mph Sign “on” time 4 seconds Detection distance 80 metres Direction targetted N b'd Monitoring loop location Distance from sign 200 metres beyond sign Effectiveness
Comments: Vehicles are detected as they approach the brow of the hill. Shorter exposure than other sites but very squarely directed at drivers. © Crown copyright. All rights reserved. Licence No. AL100021177
12 Sheet 4.3.5 Guildford Road, Chertsey
Sign Location: A320 Guildford Rd Speed limit OSGR: TQ 03332-66662 30mph Site Description Urban commuter link
Reason for installation Inappropriate speed for conditions
Installation date 19th August 2002 Activation date 28th August 2002 Sign settings Trigger speed 30 mph Sign “on” time 4 seconds Detection distance 100 metres Direction targetted N b'd Monitoring loop location Distance from sign 100 metres beyond sign Effectiveness BEFORE AFTER Difference 5 day Mean 38.45 34.17 -4.28 5 day 85%ile 43.8 39.4 -4.40 W/end Mean 41.93 37.63 -4.30 W/end 85%ile 46.9 41.6 -5.30 Comments: Highly visible. Foliage must be regularly trimmed to avoid obscuration.
© Crown copyright. All rights reserved. Licence No. AL100021177
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Sheet 4.3.6 Chilsey Green Road, Chertsey
Sign Location: A320 Chilsey Green Road Speed limit OSGR: TQ 03410-67333 30mph Site Description Urban commuter link
Reason for installation Inappropriate speed for conditions
Installation date 19th August 2002 Activation date 28th August 2002 Sign settings Trigger speed 30 mph Sign “on” time 4 seconds Detection distance 150 metres Direction targetted N b'd Monitoring loop location Distance from sign 150 metres beyond sign Effectiveness
Comments: Visible from at least 200 metres. Very good contrast with background. © Crown copyright. All rights reserved. Licence No. AL100021177
14 Sheet 4.3.7 Chilsey Green Road, Chertsey
Sign Location: A320 Chilsey Green Road Speed limit OSGR: TQ 03282-67547 30mph Site Description Urban commuter link
Reason for installation Inappropriate speed for conditions
Installation date 19th August 2002 Activation date 28th August 2002 Sign settings Trigger speed 30 mph Sign “on” time 4 seconds Detection distance 90 metres Direction targetted S b'd Monitoring loop location Distance from sign 150 metres beyond sign Effectiveness
Comments: Ideal location would have been further away from the roundabout, but local features limit location. © Crown copyright. All rights reserved. Licence No. AL100021177
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Sheet 4.3.8 Chertsey Lane, Egham, Northbound
Sign Location: A320 Chertsey Lane Speed limit OSGR: TQ 03672-69558 40mph Site Description Urban commuter link
Reason for installation Inappropriate speed for conditions
Installation date 19th August 2002 Activation date 28th August 2002 Sign settings Trigger speed 40 mph Sign “on” time 4 seconds Detection distance 100 metres Direction targetted N b'd Monitoring loop location Distance from sign 1km metres beyond sign Effectiveness
Comments:
© Crown copyright. All rights reserved. Licence No. AL100021177
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Sheet 4.3.9 Chertsey Lane, Egham Hythe, Southbound
Sign Location: A320 Chertsey Lane Speed limit OSGR: TQ 03417-71329 40mph Site Description Urban commuter link
Reason for installation Inappropriate speed for conditions
Installation date 19th August 2002 Activation date 28th August 2002 Sign settings Trigger speed 40 mph Sign “on” time 4 seconds Detection distance 100 metres Direction targetted S b'd Monitoring loop location Distance from sign 300m metres beyond sign Effectiveness
Comments:
© Crown copyright. All rights reserved. Licence No. AL100021177
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Sheet 4.3.10 Chertsey Lane, Egham Hythe, Northbound
Sign Location: A320 Chertsey Lane Speed limit 40mph Site Description Urban commuter link
Reason for installation Inappropriate speed for conditions
Installation date August 2002
Sign settings Trigger speed 40 mph Sign “on” time 4 seconds Detection distance 150 metres Direction targetted N b'd Monitoring loop location Distance from sign 80m metres before sign Effectiveness
Comments: The equipment at this location has the potential to identify speeding vehicles using ANPR technology .
© Crown copyright. All rights reserved. Licence No. AL100021177
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5. ACCIDENT BENEFITS
Since the location where the speed changes have been measured are downstream from the signs it is highly likely that speeds at the sign locations have been reduced even more.
From the speed/accident modelling work of Baruya and Finch (PTRC 1994) the accidents on a road may be predicted from: 1. 57 4.43 Cvb Ab = k V b e where:
A is the number of accidents k is a constant for the road V is the Velocity Cv is the coefficient of variation (ie mean speed/standard deviation). subscript 'b' indicates the before condition and 'a' the after condition.
The change in accidents will be:
1. 57 1. 57 4.43 (Cva - Cvb) Aa /A b =( V a / V b ) e where:
Ab is the number of before accidents Aa is the number of after accidents
Using this expression an estimate of accident benefit has been made (see Table 5 below) from the changes in mean speed and standard deviation, for the before and after situation.
It should be noted that the above model was derived from standard link sections of the highway where "interventions" were not present. An "intervention", such as a safety camera or VAS, may yield a much larger accident benefit than the above model predicts, hence the results below are an indication and possibly an underestimate.
The large scale trial prediction method (Winnett et. Al. 2002) showed that, at the 19 sites with a 30/40mph (urban) speed limit, 92.4 accidents would have been expected to occur overall in the After periods, up to the year 2000, if the signs had not been installed. The actual number of accidents occurring was 61. This difference represented a highly statistically significant reduction of 34% ( ±8%). Across all sites together, a highly statistically significant 31% ( ±8%) reduction in accidents has occurred.
19 Table 5 Accident benefits
20 Table 5. Accident benefits (continued)
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6. DISCUSSION
6.1 General observations
There are speed reductions for vehicles exposed to the sign at each sign location and at some locations there is a small reduction in speed for vehicles travelling in the opposite direction.
The variation in magnitude of the measured effect may be due to a number of factors:
• The downstream measuring location varies between sites (i.e. distance to the loops). • The measuring location may be on a slight downhill slope, encouraging vehicle speeds to pick up naturally (as at Holloway Hill). • The sign types differ (i.e. camera logos, roundels etc), so it is not a comparison of like with like. • The original speed compliance at the sites varies (i.e. some have Before speeds nearer to the speed limit). • The flow varies between sites (lower flows may encourage higher speeds). • While every attempt has been made to optimise the location of the sign, natural features of the environment may act as a constraint and consequently the effect may be less marked (e.g. Holloway Hill).
85 th percentile speed reductions as high as 5.4mph have been achieved at weekends and 4.4mph during the week (Monday to Friday).
Again, the results obtained in Runnymede are in line with the results obtained elsewhere in the UK and there is no evidence of any adverse effect due to the installations.
6.2 Guildford Road, Ottershaw - Sites 1a and 1b
This site is hazardous for both pedestrians and motorists. The two 40mph VAS have been located with the purpose of reducing traffic speeds on a blind approach to the brow of a hill where there is a car park. The car park is used by persons accessing the church and the week-day creche on the opposite side of the road.
The 85 th percentiles were originally close to the posted speed but there has been a reduction since the VAS were installed, particularly at the weekend. The weekend effect is possibly due to the increase in the free flow speeds of vehicles. These vehicles are more likely to be affected by the signs than the weekday commuter traffic which is naturally impeded by the larger flows.
6.3 Chobham Road, Ottershaw - Site 2
This site has worked well due to the very good sight line on the approach to the 30mph VAS. The 85 th percentile speed is however, still high, possibly because the road has the appearance of a 40mph urban link. It is possible that a further
22 improvement could be made, by defining the location of the 30mph limit, with a high visibility gateway.
From Table 5 it can be seen that the predicted accident reductions are high (up to 32%).
6.4 Holloway Hill, Chertsey - Site 3
The 40mph VAS is located on the brow of a hill at the entrance to a garden centre. The inductive loop speed measuring location is located on the downhill slope away from the VAS site. The initial results were not encouraging and were possibly affected by the sign having been tampered with.
The VAS was re-commissioned and the data collected again, this time with a supplementary pneumatic tube data collection at the VAS location.
The data collected at the VAS location suggests that the sign has been very effective in reducing speeds but that as the vehicles move down the hill, they marginally pick up speed.
6.5 Guildford Road, Chertsey - Site 4
This site proved difficult to monitor using inductive loops, due to the presence of high voltage power lines, occasionally corrupting the data as it was collected. As a result of this, data collection was undertaken using pneumatic tube data loggers, that are unaffected by stray electric fields.
The safety camera logo VAS has had an effect upon traffic both in the direction of influence of the sign and in the opposite direction to the sign. Research into this type of VAS has indicated that it is the one type of sign that the drivers associate with enforcement. Since the driving public have become more sensitised to the presence of camera technology and that many installations have a bi-directional capability (the camera housing can be turned around), it may explain the effect at this location.
6.6 Chilsey Green Road, Chertsey - Sites 5a and 5b
Site 5 bracketed a section of urban highway with frontages on both sides of the road and with high pedestrian movements (a school is located at the northern end). Two types of VAS were installed, a safety camera logo (northbound) and a 30mph roundel (southbound).
The 85 th percentile speed reduction has been as high as 5.3mph, bringing it down much closer to the posted limit of 30mph.
6.7 Chertsey Lane (South), Hythe - Site 6
The 40mph VAS sign has been very effective, with a predicted accident benefit of up to 37%. There is a small but significant reduction in the opposite direction (southbound), possibly due to the effect of the other VAS upstream of this site (Chertsey Lane (North), Hythe - Site 7 ).
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Again, 85 th percentiles have been brought down closer to the posted speed limit of 40mph.
6.8 Chertsey Lane (North), Hythe - Site 7
This site has performed slightly less well than site 6 above.
6.9 Chertsey Lane, Egham Hythe, Northbound
Although this sign has the capability to measure a vehicle's speed and can switch on a on a 40mph roundel if an approaching vehicle is above the speed limit threshold, it differs from the other VAS in the study in a number of respects.
Firstly, it has in addition to a standard VAS, Automatic Number Plate Recognition (ANPR), that is, the capability to digitally interrogate an image of a vehicle licence plate and store both the number and the speed of the vehicle. This information can subsequently be used for operational purposes.
Secondly, the vehicle licence plate number can be displayed in a window below the roundel, if required, in order to show the driver of the vehicle that he or she has been clearly identified. Plate 6.9.1 below illustrates how the sign would appear if it were operating with the ANPR system in the display mode.
Plate 6.9.1. How the VAS ANPR sign would appear when operational.
7. CONCLUSIONS
The results have been very encouraging with all sites showing speed reductions and some with potentially large accident benefits.
With the use of this technology, there has been concern that drivers would adapt to it with time and that speeds would gradually increase. Results from large scale evaluations do not produce any evidence that in time, drivers become less responsive to the signs, even over three or more years.
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The benefits may be summarised:
• Drivers can be influenced to reduce speed when they are specifically targeted, however, with fixed signs alone there is likely to be less effect. • VAS appear to be very effective in reducing speeds; in particular, they are capable of reducing the number of drivers who exceed the speed limit and who contribute disproportionately to the accident risk, without the need for enforcement such as safety cameras. • VAS can be operated at thresholds well below normal police enforcement levels. • Operating costs are also low.
8. REFERENCES
Barker J (1997). Trials of rural road safety engineering measures. TRL Report 202. TRL Limited, Crowthorne.
Barker J, Farmer S And Nicholls D (1998). Injury accidents on rural single carriageway roads, 1994-95: an analysis of STATS 19 data. TRL Report 304. TRL Limited, Crowthorne.
Baruya A and Finch D J (1994). Investigation of Traffic Speeds and Accidents on Urban Roads . PTRC 22nd European Forum.
Department of the Environment Transport and The Regions (March 2000). New Directions in Speed Management - A review of policy.
Farmer S A, Barker J and Mayhew N (1998). A trial in Norfolk of interactive speed limit signs. Traffic Engineering and Control 39(5), pp 287-293.
Helliar-Symons R D (1983). Automatic Close-following warning sign at Ascot. TRRL Laboratory Report 1095. TRL Limited, Crowthorne.
Helliar-Symons R D and Wheeler A H (1984). Automatic speed warning sign - Hampshire trials. TRRL Laboratory Report 1118. TRL Limited, Crowthorne.
Moore R and Christie A (1963). Research on traffic signs. Engineering for Traffic Conference, 113-122 (Road Research Laboratory). TRL Limited, Crowthorne.
Taylor M C, Baruya A and Kennedy J V (2002). The relationship between speed and accidents on rural single-carriageway roads. TRL Report 511. TRL Limited, Crowthorne.
Taylor M C, Lynam D A and Baruya A. (2000). The effects of drivers' speed on the frequency of road accidents. TRL Report 421. TRL Limited, Crowthorne.
Winnett M A and Wheeler A H (2002). Vehicle-activated signs – a large scale evaluation. TRL Report 548. TRL Limited, Crowthorne.
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Appendix A: BACKGROUND TO VEHICLE-ACTIVATED SIGNS (VAS)
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Speed management
There is a well established, positive relationship between vehicle speeds and road accidents (Taylor et al. , 2000, 2002). On rural roads, inappropriate speed for the conditions is more likely to be a factor in accidents than speed in excess of the limit. Assuming that the speed limits posted on the highways are chosen correctly, then there are safety benefits to be achieved by encouraging drivers to travel at or below the speed limit. Additionally, speed limits are by nature inflexible and there are occasions and locations along the road network that require drivers to adopt speeds that are below the posted speed, that is, speeds suitable for the local conditions.
Encouraging drivers to make sensible speed choices with regard for local conditions is particularly important, since driver error is the major contributory factor in 95 per cent of road accidents. The following observations were made in DfT's review of speed policy, New Directions in Speed Management (2000):
• Para 137: It is clear that we need a consistent strategy for managing vehicle speeds on all rural roads.
• Para 145: If we could assess the best speeds for these roads, there is still the question of how to bring vehicle speeds in line with it. There is evidence that drivers are confused about the national rural speed limit. The nature and appearance of the road is one of the strongest influences on how fast people drive, and therefore the speeds currently driven on rural roads. If a lower speed limit were imposed without any additional speed management measures, drivers' attitudes would have to change for there to be a general reduction to the new limit.
While there appears to be a very small hard core of drivers who refuse to conform both to law and common sense, research suggests that a majority of drivers may be encouraged to change their behaviour with advice that is appropriate, sensible and relevant to them in the prevailing conditions. Driver responsibility, given reasonable help, underlies much road safety policy.
An assessment undertaken on the level of accidents on rural single carriageway roads (Barker et al. , 1998) suggests that vehicle speed is an important factor. A range of rural road safety engineering measures has been developed to encourage drivers to adopt a safe speed choice on the approach to hazards such as bends and junctions (for example Barker et al. , 1997).
The ideal road safety measure would:
• Have an initial low cost, with small annual recurrent costs; • Have low maintenance and high durability; • Be self-enforcing with high compliance, and • Be without long term behavioural adaptation and consequent reduction in effectiveness.
27 Vehicle-Activated Signs (VAS) correspond closely to these requirements and during the last decade (1990s) the number of installations has been increasing in the United Kingdom. VAS is a means of delivering a simple message relating to conditions on the highway (presence of bends, junctions or speed requirements) to specific drivers. The sign activates and displays a message when a driver exceeds a particular threshold (normally based on speed).
Early work on VAS
TRL carried out research in the late 1970s and early 1980s on automatic signs that gave drivers information that related either to close following or to excessive speed. The signs remained unlit until drivers exceeded a predetermined threshold relating to either the distance from the vehicle in front or the vehicle's speed.
The sign advising drivers to 'MOVE APART' (Plate B1) was constructed using a back-lit message and relied on an overhead infra-red detector to measure the separation of the close following vehicle from the vehicle in front.
The sign advising drivers to 'SLOW DOWN' (Plate B2) had a message formed by a number of pinpoints of light individually supplied through fibre-optic cables. The vehicle speed was measured from inductive loops buried in the carriageway. The original 'SLOW DOWN PLEASE' message was later amended to 'SLOW DOWN 30'.
Plate B1. Close following sign
28 Plate B2. Speed reduction sign
The close following sign was trialled on the A332 at Ascot, Berkshire (Helliar- Symons, 1983) and the speed limit speed warning signs were trialled in Hampshire on the A32 (now B3349) at West Meon and Droxford, where conventional accident countermeasures had not been entirely successful (Helliar-Symons et al. , 1984).
The speed reductions obtained using these signs were modest but the experiment was possibly more successful than appreciated at the time. It should also be noted that the speed samples were small (around 100 drivers per sample) and that the measurements were made with hand-held radar. The measured speeds at the signs tended to decrease with time after the signs were installed, suggesting that some regular users of the roads had learned to reduce their approach speed and avoid activating the sign. The analysis indicated a halving of accidents within the speed limits following sign installation, but this reduction was not statistically significant; the numbers of accidents associated with the sites were very small.
A few years later, a similar trial of speed warning signs was carried out in Warwickshire (Long Compton) using the legends 'TOO FAST' and 'SLOW DOWN 30'. This time statistically significant reductions in speed occurred that were maintained consistently over 12 months.
The issue of trigger speeds and the corresponding proportion of the target population seemed to be of much concern at the time of this early research. There was a fear that habituation, whereby drivers become immune to the signs and thus cease to respond, would occur if too many activated the signs. This thinking was perhaps based on drivers merely processing and responding to the messages given by the signs rather than on exploring the wider cognitive processes that might be at work. The predominant effect of a vehicle-activated sign was perhaps regarded as really little different from static signing. At West Meon the speed thresholds were actually set at between the 75 th and 81 st percentile speeds which gave a very small target population. In Warwickshire the initial threshold was around the 20 th to 30 th percentile speed, thus targeting many more drivers. This produced far more encouraging results.
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The results of this early work may be summarised as follows:
For close following:
• The close following sign reduced by about 30% the number of drivers following the vehicle in front with a gap of less than one second; • The effect was maintained 800m downstream; • There was no appreciable degradation of the effectiveness of the close following sign over a five-year period.
For speed reduction:
• Measured speeds tended to decrease with time after the sign installation; • In the village centres of West Meon and Droxford, small reductions in the speeds of the faster vehicles were achieved.
Further development of VAS
The latest generation of VAS display a message (symbols and words) delineated by either fibre-optic cables or light emitting diodes (LEDs) mounted on the front panel of the sign. The sign messages, configured from fibre-optic cables, are illuminated by quartz halogen lamps and different parts of the message or symbols can be shown in different colours. The lamp is provided with an automatic dimmer to reduce the intensity during night-time operation. When not activated by a vehicle, the sign remains blank (i.e. blacked out).
The signs used recently have been of two types:
• Speed reinforcing; • Warning (for example, of a hazard).
The speed reinforcing signs display a speed limit roundel. Vehicles exceeding a pre-set threshold cause the sign to illuminate. The warning signs (used at bends and junctions for example), unlike the speed limit roundels, do not advise the driver to adopt a specific speed but rely upon their good judgement. This pre-supposes that drivers are capable of making an intelligent evaluation of a situation having been warned in advance.
TRL has conducted a number of trials on a range of vehicle-activated signs as follows:
• 30mph and 40mph roundel signs on village approaches in Norfolk (Farmer et al., 1998); • 20mph roundel sign (village centre); • Rural bend warning sign (Plate B3); • Rural junction warning sign (Plate B4); • Safety camera repeater sign (displaying warning logo).
30 Plate B3. Felbrigg bend, Norfolk
Plate B4. Felthorpe junction, Norfolk showing the sign on and off
With the exception of the rural bend sign (Felbrigg, Norfolk) that was activated from a buried inductive loop, the other signs were activated by microwave detector heads (X- band 10.5Ghz) mounted on the top of the signs. These heads were aligned to detect vehicles at a distance of 100-150m in advance of the signs.
The signs were switched on for 4 seconds when a vehicle exceeding the threshold was detected. This exposure time was calculated to be sufficient for the driver to register and understand the message. As a rule, the distance between the sign and the position at which the vehicle is detected, can be calculated from the distance travelled in 3 seconds at the 85th percentile speed. The time of 3 seconds was chosen because it was found that almost all drivers (99.9%) should be able to read a sign consisting of N words in N/3 + 2 seconds (Moore et al., 1963). This formula was derived from an experiment in which subjects had to identify a specific place name on a sign displaying a number of unrelated names. It was assumed that in the case of
31 meaningful phrases such as speed warning messages, they would be read more quickly, hence the minimum exposure of 3 seconds to the message.
The threshold speed, at which the vehicle-activated warning signs were switched on, was set at the 50 th percentile speed detected at the sign location before the sign was installed. This was to avoid excessive exposure to the sign by targeting half of the drivers - however, Norfolk County Council have reported a few queries from the public about this threshold level. The speed roundel signs did not necessarily have a threshold speed set at the actual speed limit.
Vehicle-activated roundel signs have achieved reductions in the average speed of vehicles of up to 7.5mph, with the larger speed reductions occurring at locations where speeds were higher initially. Warning signs have also encouraged speed reductions approaching hazards. There is no indication that drivers are habituating to the signs such that their speed begins to increase again over time.
The latest study of over 60 VAS (Winnett et al, 2002) shows that across all sites together, a highly statistically significant 31% accident reduction has occurred.
Summary of effectiveness of Vehicle Activated Signs
The following summary of accident benefits is drawn from the TRL Report 548.
Effect on speeds and accidents
At the speed limit roundel signs, mean speeds of the traffic as a whole were reduced by between 1mph and 14mph, the higher reductions being where the speed limit had also been reduced by 10mph. The average reduction in mean speed where there had been no change in the speed limit was 4mph (range 1mph to 7mph).
The junction and bend warning signs reduced mean speeds by up to 7mph, and the safety camera repeater signs yielded a reduction of up to 4mph. The percentage of vehicles exceeding the limit were also reduced, with the reductions tending to be greater at the roundel signs.
There has been a statistically significant one-third reduction in accidents across all of the Norfolk sites combined when compared with the number of accidents that would have been expected without the signs. Safety camera repeater signs appear to give small additional accident reductions over safety cameras alone.
Public opinions
Nearly 450 drivers took part in opinion surveys at three locations in Norfolk and one in Wiltshire. Two locations had a speed limit roundel (20mph and 40mph) and two had a junction sign. Most of these drivers drove regularly past the relevant sign. Opinions were sought about the four sign types, some of which might be thought to be associated with enforcement, by showing photographs of each type of sign. (The roundel signs were pictured with and without a microwave detector head, which could be thought to be a speed enforcement camera.)
32 There was overwhelming approval of the signs. Most drivers had made the connection between their own speed and the signs being triggered; exceeding the speed limit was thought much more likely to trigger the roundel sign than the other signs. At the locations with the junction warning sign, nearly all drivers thought that its main purpose was to slow them down or to warn of a hazard.
Over half of drivers believed they would receive a penalty for triggering the safety camera repeater sign.
These surveys suggest that the attitudes, understanding and behaviour of drivers in both Norfolk and Wiltshire are very similar and thus there is no clear regional bias.
Conclusions
• Clearly, drivers can be influenced to reduce speed when they are specifically targeted, with fixed signs alone likely to have less effect. • Vehicle-activated signs appear to be very effective in reducing speeds; in particular, they are capable of reducing the number of drivers who exceed the speed limit and who contribute disproportionately to the accident risk, without the need for enforcement such as safety cameras. • Vehicle-activated signs can be operated at thresholds well below normal police enforcement levels. • There is no evidence that in time, drivers become less responsive to the signs, even over three years. • Operating costs are also low. • In this study, a substantial accident reduction has been demonstrated.
REFERENCES
Barker J (1997). Trials of rural road safety engineering measures. TRL Report 202. TRL Limited, Crowthorne.
Barker J, Farmer S And Nicholls D (1998). Injury accidents on rural single carriageway roads, 1994-95: an analysis of STATS 19 data. TRL Report 304. TRL Limited, Crowthorne.
Department of the Environment Transport and The Regions (March 2000). New Directions in Speed Management - A review of policy.
Farmer S A, Barker J and Mayhew N (1998). A trial in Norfolk of interactive speed limit signs. Traffic Engineering and Control 39(5), pp 287-293.
Helliar-Symons R D (1983). Automatic Close-following warning sign at Ascot. TRRL Laboratory Report 1095. TRL Limited, Crowthorne.
Helliar-Symons R D and Wheeler A H (1984). Automatic speed warning sign - Hampshire trials. TRRL Laboratory Report 1118. TRL Limited, Crowthorne.
33 Moore R and Christie A (1963). Research on traffic signs. Engineering for Traffic Conference, 113-122 (Road Research Laboratory). TRL Limited, Crowthorne.
Taylor M C, Baruya A and Kennedy J V (2002). The relationship between speed and accidents on rural single-carriageway roads. TRL Report 511. TRL Limited, Crowthorne.
Taylor M C, Lynam D A and Baruya A. (2000). The effects of drivers' speed on the frequency of road accidents. TRL Report 421. TRL Limited, Crowthorne.
Winnett M A and Wheeler A H (2002). Vehicle-activated signs – a large scale evaluation. TRL Report 548. TRL Limited, Crowthorne.
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