M3 / M27 / M6 Motorway Access Management
Tools Involved
- Ramp Metering ;
Site Description
Ramp Metering (more recently termed Motorway Access Management) has been used widely across Europe and the U.S with reported success. The HA evaluated ramp metering and the benefits it can deliver by installing a pilot. The M27/M3 site was said to have sufficient slip road capacity and a regular occurrence of peak period traffic congestion required for ramp metering to operate as intended. Hence, 6 sites for the pilot were commissioned in 1998. These sites were decommissioned in 2005 when access management was no longer required on the sites. After that there were many other ramp metering schemes. However, this case study is focused on M27/M3 scheme.
Site Problems
The road capacity can frequently be exceeded due to large quantities of traffic trying to join the M27/M3. The result of this is congestion and stop-start driving conditions which increases both the risk of nose to tail accidents and journey times.
Scheme Description
The M27 Ramp Metering scheme went live in August 2000. The system works by limiting the amount of traffic entering a motorway from an entry slip road during peak times, so as to control the flow of vehicles and minimise traffic overload. It is achieved by electronically monitoring the main carriageway traffic flow and the vehicles seeking to join it. Traffic signals on the entry slip road, controlled by a set of control algorithms, are used to manage access for the road traffic.
In 2001, the existing M6 ramp metering system was upgraded to use equipment developed for use on the M27 / M3.
Scheme Objectives
The M27 access control scheme aimed to stop and start traffic entering the carriageway at the optimum timing in order to maximise throughput and therefore improve journey times, reduce accidents and minimise pollution caused by congestion.
Another key objective of the scheme was to determine the effects of Ramp Metering at different junctions and to assess, as widely as possible, the design and operational issues that might arise in any national installation programme.
Improvements
The system aimed to:
- reduce congestion caused by over-exertion of road capacity;
- improve journey times;
- reduce pollution resulting from stop-start driving conditions; and
- improve safety by lessening the risk of nose to tail accidents.
Integrated Systems
The M27 Access Management system is a stand-alone scheme; each site has a stand alone operation.
Costs
No cost information has been provided.
Benefits
Benefits from the first phase of the scheme (M27 J3 Eastbound and J7 Westbound) are shown in the table below.
Actual benefits reported |
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| Impact Assessment | Environment | No environmental benefits reported |
| Accessibility | No accessibility benefits expected or reported | |
| Safety | No safety benefits reported | |
| Efficiency | Journey times at M27 J3 eastbound improved by only 1% and the increase in slip road time (where there was a large slip road flow), had a negative impact. Vehicle counts were inconsistent between upstream and downstream detectors, preventing a final conclusion on the impact of ramp metering at this junction from being possible. Although a speed reduction was seen overall with ramp metering at J3, the speed variation was significantly larger during the ‘Off’ period. This suggests that ramp metering led to more consistent traffic condition at M27 J7 westbound worsened by 8%, with flow breakdown occurring earlier in the day and flow recovery being delayed. There was a significant increase in flow, but only between 06:55 and 07:15, after which the results were negative; this was attributed to a very rapid increase in slip road traffic. Speeds dropped earlier during ‘On’ periods than ‘Off’ periods at J7. A combination of high average free flow speeds (due to a low percentage of HGVs) and a short distance from the metering stop line to the entry point to the main line probably contributed to this result. The main reason behind such discouraging results was believed to be a lack of sophistication in the ramp metering control algorithms. These were approximations of internationally recognised control algorithms such as ‘ALINEA’ and ‘Demand Capacity’, which resulted in a less effective operation. |
|
| Integration | No integration benefits expected or reported | |
| Technical Performance | No technical performance benefits reported | |
| User Acceptance | No user acceptance research was carried out | |
Results from the upgraded M6 system are shown below:
Actual benefits reported |
||
| Impact Assessment | Environment | No environmental benefits reported |
| Accessibility | No accessibility benefits expected or reported | |
| Safety | No safety benefits reported | |
| Efficiency | Average flow increase of around 5% was acheived during some periods at the M6 test sites (J10, J9 and J7 Southbound). The impact of ramp metering on average speed was greater than the impact on average flow. Average speed was increased by 14% and 18% upstream of J9 and J7 Southbound respectively. The peak period was shortened with Ramp Metering by twenty minutes at M6 Junction 7 Southbound. On average flow breakdown was delayed by ten minutes and speed recovered ten minutes earlier. |
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| Integration | No integration benefits expected or reported | |
| Technical Performance | No technical performance benefits reported | |
| User Acceptance | No user acceptance research was carried out | |
Summary of Benefits Information:
These results show that the benefits of ramp metering are extremely sensitive to the installation location. The Highways Agency "Interim Advice Note Regarding the Assessment of Ramp Metering" should be used to determine sites suitable for the installation of Ramp Metering.
No attempt has been made to validate the results reported. Users of the guidance are encouraged to assess the robustness of the results presented and the likely transferability of the case study to their own local environment.
