Advanced motorway signalling and traffic management feasibility study (HTML version)
2 The M42 Active Traffic Management Pilot
2.1 The M42 pilot provides vital evidence for any wider roll out of advanced motorway signalling and traffic management technologies. Accordingly, this chapter of the report sets out the experience of the pilot in some detail, together with the findings which emerged.
The decision to pilot hard shoulder running
2.2 In 2001, the then Secretary of State asked the Highways Agency to trial hard shoulder running on the M42 between junctions 3A and 7, to the south-east of Birmingham, with the following objectives:
- To optimise safety and performance, in accordance with the volume and make up of the traffic;
- To provide more consistent journey times;
- To minimise harmful emissions and fuel consumption;
- To reduce delays and disruption due to accidents and incidents; and
- To provide improved warnings and traffic management in association with routine maintenance operations.
2.3 Phased operation began in January 2005 and dynamic peak period hard shoulder running was implemented in September 2006.
Figure 2: M42 pilot scheme route
2.4 This section of the M42 was chosen for the pilot because it suffered from typical problems which it was envisaged hard shoulder running would be able to tackle. The route has high traffic flows and encompasses interchanges for the National Exhibition Centre and Birmingham International Airport, with very significant peak period commuter flows. The site has well defined morning and evening peaks which suited the dynamic operation of the hard shoulder. In addition, local traffic was already familiar with lane signals and tidal flow on the A38(M) Aston Express Way.
The pilot system
2.5 The M42 pilot provided the opportunity to demonstrate and test a number of dynamic traffic management tools, positioned and utilised according to best practice, comprehensive safety hazard analysis and pre-determined operational regimes. The system includes:
- lightweight gantries with Variable Message Signs around every 500m;
- appropriate road markings and fixed signing;
- continuous safety fencing;
- Pan Tilt and Zoom (PTZ) cameras;
- fixed CCTV cameras typically up to 250m intervals;
- semi-automatic control system (SCS);
- HADECS cameras;
- lighting throughout the length of the scheme; and
- the necessary optical fibre cabling and communications links.
2.6 This infrastructure allows the hard shoulders to be used as running lanes. This was implemented initially only during maintenance and incidents to prove that the concept was workable and was followed by full-scale operation of peak time hard shoulder running, with the full involvement of the emergency services.
2.7 MIDAS detector loops in the carriageway measure traffic flow and as certain traffic levels are reached, a variable speed limit is automatically displayed above the lanes. When appropriate, the hard shoulder can be opened to traffic, to minimise congestion. When the hard shoulder is in use, a maximum 50mph speed limit is applied across all lanes. This speed was adopted for the purposes of the pilot as it balanced the need to improve journey times and reliability, whilst ensuring at least the same levels of safety. In respect of both the operating parameters and the equipment specification, a precautionary approach was adopted, as deemed appropriate for pilot implementation.
Figure 3: Hard Shoulder Running on M42
2.8 In order to ensure the high levels of compliance with speed limits necessary to achieve the benefits of hard shoulder running and maintain safety, the Highways Agency worked closely with the police to provide enforcement for traffic management purposes. The police use HADECS cameras to maintain compliance.
2.9 Safety was a key aspect of the design parameters adopted for the pilot. Emergency Refuge Areas are provided around every 500 metres, to provide a safe place to stop away from traffic. Comprehensive CCTV coverage enables Traffic Officers in the control room to spot any incident or breakdown on the carriageway and protect the incident by closing the affected lane immediately using overhead signs. The capability to open and close lanes means that in the event of a major incident, lane closures can enable emergency services access as quickly as possible - however, to date there have been no incidents of sufficient severity to warrant the use of this capability. As such it has not been operationally tested and the arrangements could possibly increase usual response times.
The results of the pilot
2.10 The pilot was successful in reducing congestion, improving the predictability of journey times and increasing motorway capacity, with consistent results throughout the first six month trial period.
2.11 Three time periods were used for comparing the results of the pilot:
- baseline (the before situation) – the period June 1998 to June 2003;
- intermediate – the period from January 2006 to June 2006 during which the M42 between Junctions 3A and 7 was operating as a Controlled Motorway, without hard shoulder running, and
- the pilot period itself – the 6 months from October 2006, when hard shoulder running was in operation when required.*
*Although hard shoulder running went live in September 2006, the monitoring period officially began in October 2006. This allowed for a ‘settling in’ period following introduction of the new scheme.
2.12 The performance of the pilot over the 6 month period can be analysed under the following headings:
- traffic flow and throughput
- journey times
- journey time variability
- emissions and air quality
Traffic flow and throughput
2.13 During the first 6 months, the pilot scheme coped with consistently high levels of demand by utilising the hard shoulder as a running lane when required. Analysis shows little variation in demand between months during the trial period. The pilot section saw average traffic flows of 130,000 vehicles per day (140,000 on typical week days), a significantly higher flow than the national motorway average of around 96,000.
2.15 Journey times during Friday afternoon peaks, when disruption to customers is at its worst on this part of the motorway, show a significant improvement when hard shoulder running is in operation. The afternoon peak average journey times on Tuesdays to Thursdays have reduced by an average of 26% northbound and 9% southbound when compared to the intermediate period. This equates to an average reduction of 4 minutes northbound and 1 minute southbound. Overall however, drivers have a slightly longer journey on the M42 with hard shoulder running, due to the reduced speed limits in operation.
Journey time variability
2.16 The journey time is, however, much more predictable. Hard shoulder running demonstrated, on average over all weekdays, a reduction in the variability of journey times of 27% and 34%, when compared to baseline and intermediate states respectively.
2.17 This enables the travelling public, freight operators and business users to plan their journeys more effectively, with greater confidence that they will complete their journey through the pilot section within a pre-specified timeframe.
2.18 Speed compliance on the main carriageway was on average:
- 94% or better at the 70 mph, 60 mph, 50 mph speed limits
- 87% or better at the 40 mph speed limit.
2.19 Compliance on the hard shoulder was on average:
- 98% or better at the 50 mph speed limit
- 93% or better at the 40 mph speed limit.
2.20 These high levels of compliance have remained almost constant through the intermediate and pilot periods. Safety
2.21 Safety is discussed in greater depth in chapter 3 of this report. Briefly, no evidence emerged from the pilot which suggests that hard shoulder running may have an adverse effect on safety. Personal injury accidents dropped from an average of 5.2 per month over the five year "before" period to 3.3 per month in the 6 month intermediate period, and subsequently during the 6 month pilot period to 1.5 per month.
2.22 However, owing to the relatively short period of monitoring, we cannot be certain that the reductions in accident rates are attributable to the traffic management system itself. Further observation is ongoing. The first 10 months of operation have seen 16 personal injury accidents, 4 of which occurred during hard shoulder running, giving a slightly increased average rate of 1.6 per month when compared to the 6 month results (but still below the "before" situation).
2.23 The overall noise assessment of the M42 scheme has shown that average noise levels according to the standard UK index have been reduced by between 1.8 to 2.4 dB(A), data which has been 'normalised' to remove the increase from the higher flow. This was to isolate the effects of hard shoulder running (i.e. to confirm that running on the hard shoulder did not make noise worse because traffic is closer to the road boundary and to identify any improvements from smoother flow). Noise per vehicle was therefore shown by the noise assessment to be reduced. However, this effect could be negated by a significant increase in traffic generated by the scheme. Therefore this noise result was classified a negligible/minor benefit for the purposes of environmental noise assessment.
Emissions and air quality
2.24 The effects on vehicle emissions between winter 2003 and winter 2006 (all vehicles types) of the pilot scheme were:
|- CO reduced by 4%||- PM reduced by 10%|
|- HC increased by 3%||- CO2 reduced by 4%|
|- NOx reduced by 5%||- fuel consumption reduced by 4%|
2.25 However, these results reflect changes in individual vehicle emissions and do not take into account the effects of any overall increases in traffic that may have come about as a result of the scheme. The various emissions effects of hard shoulder running are further discussed in chapters 4 and 6 of this report. The reductions in vehicle emissions are similar to those identified by two studies of the impact of Controlled Motorway operations on the M25. It was not possible to isolate the effects of hard shoulder running on air quality, because the system is only one of a number of factors which will have influenced changes in ambient air quality in the locality of the pilot between 2003 and 2006.
2.26 The carbon impacts associated with the construction and running of hard shoulder schemes are discussed in chapter 4.
The costs of the pilot
2.27 The costs associated with delivering the M42 pilot are shown in figure 4 below.
Figure 4: M42 pilot costs
|Cost Element||Cost £m|
2.28 This equates to a cost per km of motorway (both carriageways included) of £5.6m (outturn costs - covering the total cost of all of the design, development, delivery, construction, infrastructure and support costs from inception to maintenance handover). In addition to these costs, there were also costs associated with the pilot's communications campaign, of approximately £300,000 (plus VAT). By way of comparison, the costs of conventional widening the same section of the M42 from 3 lanes to 4 in each direction have been estimated at between £18m and £25m per km of motorway, at current price levels.
2.29 There are 17 hard shoulder running schemes in the Netherlands, 6 in Germany (covering 200km) and one in Virginia in the USA. These schemes differ somewhat in design and operation from the M42 scheme, but generally they show similar benefits. The Netherlands schemes have increased capacity by between 7% and 22%. Travel time savings range from 1 to 3 minutes, journey time reliability has improved significantly and there has been no negative impact on road safety. Results from Germany and the USA similarly show no negative impact on road safety, but improvements in journey times and traffic flows. The experience in the Netherlands was used to inform the design of the M42 pilot scheme, however, the legal and safety standards and the approach to pilots differs considerably between the two countries, so the schemes are not directly comparable in all respects.
Summary of conclusions
2.30 The M42 pilot has given us valuable experience of installing and operating a hard shoulder running system in the UK, and early results indicate benefits in relation to traffic flow, journey time reliability, emissions and compliance at considerably lower cost than widening schemes. We should look to learn from and build on this experience in implementing similar schemes in the future.