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M4 Junctions 24 - 28 Variable Speed Limit Scheme

www.wales.gov.uk

www.traffic-wales.com

The M4 Variable Speed Limit Scheme in Wales

The M4 South East Wales variable speed limit scheme is on course to begin operation in spring and summer 2011. It will make use of the latest technology to tackle congestion on the 13km stretch from the M4 Junction 24 (the Coldra) to Junction 28 (Tredegar Park).

The scheme’s underlying principle is to keep traffic moving by adjusting the speed limit, helping to make journeys safer and more reliable.

The Welsh Assembly Government is leading the project through Traffic Wales, its traffic management and information service, whose control room team will operate and monitor the new system from the South Wales Traffic Management Centre in Coryton, Cardiff.

The variable speed limit scheme is part of a wider Welsh Assembly Government programme to improve major road links across Wales. It aims to effectively manage the strategic road network now and for the future, encouraging inward investment, growth and jobs.Yo

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Why does this section of the M4 need to be improved?

As this stretch of motorway serves not only Newport but wider connection routes across South Wales and into England, it is essential that it works efficiently.

At present, the section is vulnerable to congestion build-up as traffic flows exceed capacity (the approximate average traffic flow is 2,188 vehicles per lane per hour compared with 1,800 vehicles recommended by design standards). Combined with varying gradients and tight bends that reduce visibility for the driver, the level of congestion contributes to a local accident rate higher than the national motorway average, which included nine fatalities between July 2006 and June 2009. As well as the obvious safety concerns, the high traffic volumes and accident rates cause delay in the surrounding area, significant fluctuations in journey times and a reduction in air quality.

Why isn’t the motorway being widened?

There is little scope for constructing additional motorway lanes in the area due to the proximity of housing and the position of the 1,200-foot-long Brynglas tunnels between Junctions 25a and 26.

The introduction of a variable speed limit provides a viable alternative solution to address the issues. It is quicker to implement and is a more cost-effective option for delivering improvements than road widening, with construction estimated at £7million. It also has less of an environmental impact as construction is confined to the existing highway.

What benefits will the variable speed limit scheme bring on the M4?

The scheme is expected to deliver the following benefits:

• Reduction in congestion

• Reduction in accident rates by around 13%

• Improvement in journey time reliability

• Improvement in air quality through reduction of sudden and heavy braking

• Improvement in driver comfort

• An increase in throughput of traffic over the controlled section leading to an increase in motorway capacity

• Estimated savings of £40million over the next 30 years through a reduction in accidents and an increase in journey time reliability

Variable speed limits have been part of many successful and safely-operated schemes on the M25 and M42. These have seen journey time reliability increase and accident rates fall. This experience gives us confidence that we can do the same for this section of motorway in Wales.

How the scheme will work

How will the variable speed limit scheme work?

Through this section of motorway, the mandatory speed limit will be adjusted according to traffic conditions to keep vehicles moving at a steady rate. At times of heavy traffic flow or in the event of an incident, sensors located beneath the surface of the road will detect congestion beginning to build up. The system will calculate the optimum speed limit which will be displayed on electronic signs over each lane. The 70mph national speed limit will apply when there are no incidents and when there is no congestion on the motorway.

Adherence to the variable speed limits will result in vehicles travelling at more constant and similar speeds. This will reduce queuing and the associated risk of collisions occurring as vehicles approach the back of queues.

With the body of traffic travelling at a steady speed, congestion in the outside lane is reduced. This delivers an increase in motorway capacity without the need to construct extra lanes.

Who will monitor the variable speed limit scheme and when will it come into operation?

Initially, the variable speed limit scheme will be manually operated by Traffic Wales. Control room operators will monitor traffic conditions, adjusting the speed limit and other signs as required. West of the Brynglas tunnels up to Junction 28, this will begin in March 2011. The remaining section east of the tunnels up to Junction 24 will follow in summer 2011 on completion of a separate project to replace the central reserve barrier in this section of motorway.

Automatic variable speed limit operation that makes full use of the scheme’s technology is expected to begin in autumn 2011. Traffic Wales’ operators will continue to monitor the scheme and will intervene when incidents occur to display advance warning messages on signs on the approach to the scene.

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Completion summer 2011 – new superspan gantries with message sign and speed limit displays

What visible changes are there to equipment on the roadside?

Many of the physical features of the variable speed limit scheme are already familiar to motorway users.

Overhead ‘gantry’ structures (as pictured in the diagram below) are in use throughout the motorway network. Within the variable speed limit section, these house electronic signs displaying the speed limit over each lane. Thirteen existing structures have been refurbished for use in the scheme. In addition, five ‘superspan’ gantries that stretch across the entire width of the motorway have been constructed.

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Variable message signs already used extensively on the motorway network will provide traffic information via text and picture messages. A number of these feature on overhead gantries (as pictured on the previous page). Five new message signs have also been installed on the roadside (pictured below).

Reduced sized message signs (pictured below) are positioned in the verge, spaced 250m to 700m apart. The signs will repeat the speed limit displayed overhead and serve as reminders of the limit in force at the time. They are installed on innovative wind-down poles designed to be rotated and lowered, enabling access for maintenance teams from behind the roadside safety barrier. This reduces the need for lane closures when access is required and has the advantages of preventing disruption to the public and reducing maintenance costs.

Those joining the M4 via slip roads in the area will see electronic signs mounted on posts (as pictured below). These will indicate the speed limit in force on the motorway at the time.

Will there be any difference as to how the emergency services can reach an accident?

The emergency services will continue to have priority use of the hardshoulder in the event of an incident. Clearer access has been provided around the Brynglas tunnels which will assist the emergency services in reaching incidents quickly.

Temporary restrictions

Why is there currently a 50mph speed limit between Junctions 24 and 28?

A separate Welsh Assembly Government project is underway to replace the central reserve barrier on this section of motorway. A temporary 50mph speed limit is to remain in place for the duration of construction works to maximise the safety of road workers and motorway users. The 50mph limit will be removed following the completion of the new concrete barrier (expected west of the Brynglas tunnels in March 2011 and east of the tunnels in summer 2011), when variable speed limits will take over.

The infrastructure installed for the variable speed limit scheme will be utilised as fully as possible in the meantime to promote the safety of the travelling public and road workers.

A refurbished gantry in the variable speed limit

Have the public been told that the 50mph speed limit is temporary?

The temporary 50mph limit between Junctions 24 and 28 came into force on 6th April 2009. The proposed limit order was published in advance as part of the statutory process and clearly stated that the limit was temporary.

Temporary traffic signs on the M4 indicate the section over which the 50mph limit applies.

The wind-down Verge Mounted Cantilevered pole with reduced sized message sign

Electronic post-mounted sign

A new variable message sign on the roadside

Average speed cameras have been installed on this section. How do these work and will they be used to enforce the variable speed limit?

Average speed cameras are in place to help enforce the temporary 50mph speed limit. The cameras continually capture images of vehicles as they pass between Junctions 24 and 28. They use Automatic Number Plate Recognition to detect and calculate the average speed of each vehicle. If the speed limit is exceeded, an offence is recorded. Offenders are then subject to prosecution by the police by way of fixed penalty, court processes or completion of a speed awareness course.

The average speed between Junctions 24 and 28 before the introduction of cameras was 58.5mph. This fell to 49.4mph following the installation of speed cameras in September 2009, demonstrating the cameras play a role in encouraging compliance with the speed limit.

When the variable speed limit comes into operation, new speed enforcement cameras will be installed.

Environmental issues

What impact will the scheme have on the environment?

The findings of the scheme’s Environmental Assessment Report are summarised in the paragraphs below. A Record of Determination (summarising the report) is available on request from the Welsh Assembly Government. No statutory Environmental Impact Assessment was required on this scheme.

Adherence to an Environmental Management Plan was among the methods used to limit any impact while works were in progress.

Does the variable speed limit scheme installation have an effect on the landscape?

The majority of changes do not impact on the landscape as many views in the area are already largely dominated by the motorway and associated infrastructure. Installation of ‘superspan’ gantries has a slight effect on the landscape around Junctions 25a, 26 and 28. Further landscaping to provide screening from the motorway is restricted as the surrounding area is largely urban and narrow.

Are nature conservation areas, vegetation and habitats affected?

Strict pollution control measures avoided any impact upon designated nature conservation sites or local habitats during construction.

Although the scheme required the removal of some vegetation within the highway boundary, any with landscape or nature conservation value was retained where possible. The size of work areas was minimised to limit site clearance and ground or vegetation disturbance and re-planting was undertaken. In addition, no large scale vegetation clearance took place during the bird breeding season.

Replacement tree and shrub planting was targeted to replace any protected species’ habitats and to lessen the visual impact of removal. There has also been natural re-colonisation of native flora. Specific plantation was chosen to favour the habitation of dormice that reside around some of the M4 structures.

How was water quality and drainage impacted?

The adoption of Environment Agency pollution control guidelines protected water quality and limited disturbance to wildlife during construction.

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Will there be improvements in air quality?

The expected reduction in congestion is likely to lead to a fall in emissions once the variable speed limit scheme is fully operational.

Are any sites of cultural significance adversely affected?

There is no physical impact on archaeological remains, as all construction took place within existing highway boundaries. Some views from Tredegar Park and the Monmouthshire and Brecon Canal are slightly affected by new infrastructure.

Will there be a decrease in traffic noise?

Once the scheme is fully operational it is expected that more efficient running of traffic will lead to a reduction in traffic noise and vibration. However, periodic queues at the Brynglas tunnels (due to the legal obligation to prevent traffic building up in a tunnel) may lead to short term increases in traffic noise.

Has any more motorway lighting been installed?

No. Some existing lighting on overhead gantries has been replaced with more efficient systems. This will reduce energy consumption and minimise light pollution beyond the sign area.

Are pedestrians, cyclists and equestrians affected?

All of the existing public rights of way in the vicinity of the motorway remain unchanged and as such there will be no disruption to walkers, cyclists or horse riders.

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The sole responsibility of this publication lies with the author. The European Union is not responsible for any use that may be made of the information contained therein.