Effective road and traffic management

Written evidence from the Transport Research Laboratory (TRL) (ETM 07)

The extent to which road user culture and behaviour undermines effective traffic management, including the relevance to day’s road user of the highway code.

1. Safety for all road users is the highest priority for traffic management. The second highest priority is to achieve the most efficient roads that enable users to travel at their desired speed or if not, to have reliable journey times. This must not compromise the first priority. To achieve these priorities, new traffic management schemes must be intuitive such that they are adopted safely and appropriately by drivers. The majority of drivers do not take active steps to be trained in use of the road after licence acquisition and the developments in the licensing process (such as hazard perception tests and theory tests) mean that there is wide variety in the level of knowledge about use of the road across the driving population. Drivers become entrenched in their driving behaviour and may be not respond to traffic management features in the expected manner. Novel traffic management schemes must therefore be tested to ensure that the predicted behaviours are observed.

2. TRL has conducted numerous studies that investigate how proposed traffic management measures affect driver behaviour. Using the validated, high fidelity research driving simulator, drivers can be presented with new features in a naturalistic yet completely safe manner and their resultant behaviour examined in great detail. This enables traffic management designs to be tested in a manner that may be impractical, unsafe or too costly to test by any other means.

3. Examples of where this process has been applied include studies of the use of high occupancy vehicle lanes, hard shoulder running, single lane tolling, use of emergency refuge areas and behaviour through temporary traffic management schemes. As an example, the results of the hard shoulder running study demonstrated that drivers used the hard shoulder when it was opened as a normal running lane for longer and more confidently when a positive signal (a red X over the hard shoulder) was used to indicate when it was not open as a normal running lane. Similarly, the Highways Agency were provided with information about driver behaviour when entering, stopping within and leaving emergency refuge areas to improve their design.

4. The Managed Motorway concept uses a variety of tools to reduce congestion and improve journey time reliability. By using TRL’s driving simulator, driver behaviour in response to different aspects of the Managed Motorway schemes has been tested providing the Highways Agency with confidence in designs that they may choose to implement.

5. The use of the driving simulator to conduct studies examining traffic management measures has enabled the Highways Agency to make efficient, evidence-based decisions about infrastructure developments before they are applied in the real world.

6. The driving simulator was also used in a study for Transport for London to examine the effects of video billboard advertising. The report demonstrated that drivers were significantly more distracted by video adverts and provided reliable evidence for TfL in responding to requests to install such advertising in conspicuous positions near busy roads.

7. The effects of fatigue on driving behaviour result in it being a contributory factor in a significant number of collisions. TRL have conducted reviews for the Department for Transport into the incidence, extent and effects of this problem.

Intelligent traffic management schemes, such as the scheme which has operated on the M42, and their impact on congestion and journey times:

8. Over the past decade, significant advances have been made in the exploitation of on-road technology to tackle congestion on the strategic road network by making best use of the existing road space and managing traffic intelligently. The M25 Controlled Motorways and M42 Active Traffic Management pilots have proven successful at smoothing traffic flows and reducing congestion at hot spots on the network. The success of these schemes has led to a programme of Managed Motorway schemes to be rolled-out across the network in coming years.

9. The M25 Controlled Motorways scheme first introduced variable mandatory speed limits (VMSL) on a motorway. Monitoring and evaluation between 1995 and 2002 found that:

1. Despite an increase in traffic levels, the amount of queuing has reduced and the number of shockwaves has decreased between 1995 and 2002 from typically 7 to 5 in the AM peak. Also noted is more balanced lane utilisation and a reduction in very short headways (References 1, 2)

2. During the AM peak the total throughput has increased by 1.5% per year and peak 1-hour throughputs have reduced by 1% per year (Reference 3).

3. On non-congested sections, VMSL will increase journey times, but leads to improved speed compliance and journey time reliability (Reference 2)

10. The M42 Active Traffic Management (ATM) pilot implemented VMSL in conjunction with dynamic use of the hard shoulder during periods of congestion or incidents. The scheme was opened for operation in March 2003, with full operation of 4-Lane VMSL commencing in September 2006. The outputs from a 12-month Monitoring and Evaluation period between 2006 and 2007 were published in 2007 (Reference 4) and include a comparison between the operation of 3-Lane VMSL between January and August 2006, and the case of no variable speed limits (VSL) prior to construction of the ATM scheme in 2002-2003. The key findings build on those reported for the M25 Controlled Motorway and are detailed in paragraphs 11 to 19 below:

Impact on traffic flows:

11. During 4-Lane VMSL, traffic congestion and the speed differential between lanes are reduced and there is a higher occurrence of free driving conditions (e.g. headways over 5 seconds). This indicates that 4-Lane VMSL leads to a lower workload for drivers. (Reference 4)

12. 4L-VMSL has improved the distribution of traffic between lanes, which is an indication of a better utilisation of the motorway. (Reference 4)

13. The operation of 4-Lane VMSL on the M42-ATM section has increased the observed capacity of the motorway by an average of 7% (compared to no VSL) and 9% (compared to 3-Lane VMSL). In general across the defined peak periods, analysis shows that there is spare capacity during 4-Lane VMSL operation. (Reference 4)

14. Speed limit of 50mph was the main contributor to modified traffic flow behaviour that could be exploited towards more efficient flow. 60mph has a rather moderate impact. 40pmh is used at high occupancies in interest of safety rather than flow efficiency.

Benefits to road users: Journey times

15. Due to the increase in demand and the introduction of variable mandatory speed limits with high compliance, there was an increase in average journey times of 9% between the no VSL and the 4-Lane VMSL cases. However, the analysis of secondary indicators has shown that 4-Lane VMSL prevented the occurrence of low speed levels and severe congestion. Therefore at the level of demand where it exceeds motorway capacity during no VSL (i.e. during recurrent severe congestion), 4-Lane VMSL will reduce the average journey times (Reference 4).

16. Compared to the 3-Lane VMSL case, 4-Lane VMSL has reduced average journey times during periods of recurrent severe congestion by up to 24%. (Reference 4)

17. Hard Shoulder Running (HSR) at 60mph reduces average journey times by 4% compared to HSR at 50mph. HSR at 60mph has increased average traffic speed by 5mph. (Reference 5)

Benefits to road users: Journey time variability

18. For 4-Lane VMSL, on average over all weekdays the variability of journey times has been reduced by 22% and 32% when compared to no VSL and 3-Lane VMSL respectively. (Reference 4)

Public perception of congestion

19. User consultation has shown that an extra 7% of users encountered no congestion on the M42-ATM section in 2007 compared to 2003. Further road user surveys conducted in connection with the pilot revealed that 68% felt more informed about traffic conditions. (Reference 4)

The impact of bus lanes and other aspects of road layout

20. Road capacity is limited and effectively shared by road users. At low flows delays to all vehicles are relatively small. However, as flow approaches capacity traffic delays and queues increase. The main limiting factor on capacity occurs at junctions where it is shared by more than one road. Bus lanes, high occupancy lanes, shared use lanes (e.g. with heavy goods vehicle) all have the same underlying purpose. This is to re-allocate the available capacity to specified "priority" vehicles included in the scheme. It will therefore aim to reduce the delay and increase speeds of these vehicles. Further, of particular importance to bus services, is the improvement to reliability of journey times. One of the main aims of such improvements is the relative improvement of the mode which can increase use, i.e. bus patronage.

Effect of bus lanes

21. An important aspect of a bus lane is the distance it is set back from the junction: i.e. the distance between the end of the bus lane and the junction’s stop line. If it is too close to the junction then although buses will gain a journey time advantage, other traffic will be greatly delayed owing to the reduction in junction capacity, and this can be counter-productive as if the non-priority traffic queue increases beyond the start of the bus lane, it can prevent buses using the lane. Too far back and the bus lane will result in little benefit for buses. There is therefore a balance to be found.

22. The results in paragraphs 23 to 27 have been collated from previous research to indicate the ability of such schemes to deliver benefits to priority vehicles and their effect on other non-priority road users. Reference 7 was a literature review on the subject.

23. Three major changes were made to the road network along Shepherd's Bush Green Road in 1993, including a bus lane, pre-signals and a bus gate. Afterwards, buses mainly ran closer to their timetables over the section of the routes surveyed, and there was less variability in departure times. Improvements of up to 55.3% (1.5 minutes) in the difference between actual and scheduled departure times were observed (Reference 6).

24. Bus lanes do not necessarily deliver observable improvements to bus journey times or reliability. A scheme in Birmingham found no significant improvements in bus arrival times at their destination, or improved regularity in bus headways were found (Reference 6).

25. Overall, bus priority schemes in the United Kingdom have previously been found to have only managed to reduce bus journey times by one or two minutes, and have not made them faster than travelling by car (Reference 6). Changes in patronage due to a bus lane alone were found to be generally small in a literature review. In six references where it was not affected by other factors the lane only stemmed an overall decline in two cases and increased patronage by 5 to 6 percent in three others (Reference 6).

26. However, large scale bus priority measure along a corridor have been found to create journey time improvements. A scheme on the A47 Hinckley Road in Leicester introduced bus lanes over 4.5km (Reference 7). The bus priority measures had a minimal effect on car journey times; during the morning peak they dropped by 5% in the inbound direction and during the evening peak they increased by 2% in the outbound direction. But there were significant improvements in bus journey times; a 22% drop in the AM peak (from 23 to 18 minutes) and 23% in the evening. Limited stop park and ride buses can cover the distance to and from the city centre nearly one and a half minutes faster than a car.

27. A combination of bus improvements can have a greater effect. The West Midlands Bus Showcase included introducing bus lanes in addition to increasing service frequency, improving bus stops, introducing real time information and strict enforcement of stopping restrictions. The effects of these enhancements have varied between routes, but bus patronage increased a maximum 38%, and there was a 5 percent mode shift from the car (Reference 8).

Shared use of bus lanes

28. Permitting heavy goods vehicles into two bus lanes in London had no effect on bus operations or safety: the conditions observed were low bus flows (up 20 per hour) and moderate heavy goods flows (up to 60 per hour) and 55% of link capacity in use. However, many heavy goods vehicle drivers did not use the lane as it did not offer a journey time saving (Reference 9))

29. Motorcycles were permitted to use bus lanes in London. This should permit them the same benefits as buses. The scheme was monitored, and it was found that bus speeds were unaffected and motorcycle speeds increased, and there was an increase in the percentage of motorcycles exceeding the speed limit. Also, collisions involving motorcycles and cyclists had increased, which were generally with cars and through poor observation.

Other aspects of road layout (with respect to buses)

30. Research into the effect of removing bus lay-bys found that buses were able to stop close to the kerb at virtually all stopping events at some sites, and this was accompanied by fewer passengers needing to step into the road when boarding and alighting. Passengers were able to board the buses faster. Fewer buses were hemmed in by traffic and overall the reduction in bus delay at a stop ranged from 2 seconds to 4 seconds depending on traffic flow. The variation in the stop time of buses was also reduced (References 10).

31. Research into introducing bus boarders found the percentage of buses stopping close to the kerb increased, and resulted in significantly fewer passengers stepping into the road when boarding and alighting (Reference 10). There was a slight reduction in boarding and alighting times of 0.1 seconds and fewer buses were hemmed in by general traffic at the full width boarder sites. Overall bus delays were reduced by 1.3 to 1.8 seconds.

References

1.

McCabe et al (2006). A flexible approach to motorway control. http://www.atkinsglobal.com/Images/A%20flexible%20approach%20to%20motorway%20control_tcm12-6205.pdf

2. Highways Agency (2007). Monitoring of the M25 Controlled Motorway: Summary Report. http://www.highways.gov.uk/knowledge_compendium/assets/documents/Portfolio/CMBC%20Final%20Summary%20Report%20-%20431.pdf

3. Rees, T et al (2004). Speed Control and Incident Detection on the M25 Controlled Motorway (Summary of Results 1995-2002). TRL Published Report PPR033. Final Version.

4. Mott MacDonald (2007). ATM Monitoring and Evaluation 4-Lane Variable Mandatory Speed Limits: 12 Month Report (Primary and Secondary Indicators). Report reference 203754_MM_007_V3, DOC/1807/V3. Final Version.

5. Ogawa, M et al (2010). M42 Active Traffic Management Monitoring & Evaluation: Results from HSR up to 60mph. Road Transport Information and Control Conference and the ITS United Kingdom Members’ Conference (RTIC – 2010) – Better Transport Through Technology, 25 - 27 May 2010, pp1 – 6.

6. York (1996). The effect of bus priority on patronage: a literature review. TRL Report PR/TT/068/96.

7. University of Leeds (2010)

http://www.konsult.leeds.ac.uk/private/level2/instruments/instrument041/l2_041c.htm.

(Accessed in December 2010)

8. PTEG (2005).

http://www.pteg.net/NR/rdonlyres/BBE4D6D8-5732-4B1E-92DD-B8C52C2D77D1/0/20051219Busbriefing.pdf

9. York et al (2003) Potential Impacts Of Heavy Goods Vehicles Using Priority Lanes: Final Report. TRL Report PR/T/124/03

10. TfL (2006). Bus stop design guidance.

http://www.tfl.gov.uk/assets/downloads/businessandpartners/accessibile_bus_stop_design_guidance.pdf

January 2011