New tunnel option for UK traffic blackspot
Mar 2012
Peter Kenyon, TunnelTalk
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Brynglas tunnels do not comply with 2014 EU Tunnel Safety Directive
- Construction of a new tunnel at Brynglas is among proposals being considered by the Welsh Government to cut accidents and improve traffic flow on the M4 near Newport in Wales.
- A public consultation document (M4 Corridor Enhancement Measures), based upon four possible solutions for easing flows and cutting accident rates between junctions 23 and 28, was published earlier this month. The new alignments, including the new tunnel solution, have been drawn up by engineering consultant Arup.
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Existing M4 and local road networks around Brynglas Tunnel
- One factor that might steer planners towards a £550 million lane-widening plan (incorporating a new tunnel at Brynglas to carry an extra four lanes) is that "significant maintenance works" are needed at the existing tunnels to bring them in line with the 2014 EU Tunnel Safety Directive.
- Because the M4 is part of the Trans-European Road Network (TERN), the 365m dual two-lane traffic tunnels at Brynglas, opened in 1959, are covered by minimum safety standards laid down in a 2004 EU Directive. These become retroactive in 2014.
- The Welsh Government admits: "The maintenance work needed to comply with the 2014 Tunnel Directive is likely to take months, if not years, to complete."
- The major obstacle against so-called Option-D is that lane widening and a new tunnel could necessitate a significant number of compulsory purchase orders. When the original tunnel was bored in the 1950s a number of houses on the hill above had to be demolished and there were a series of long-running battles in Parliament over compensation packages.
- Another option (Option-A) is to build a new 15km relief road between junctions 23 and 29. This would allow longer distance England-Wales traffic to avoid the Brynglas tunnels, one of several places on the existing M4 stretch where three-lane traffic is forced to bottleneck into two lanes.
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Option D – M4 widening and new tunnel
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Option A – New 15km southern relief road
- This plan was shelved in 2009 on cost grounds, and according to the latest consultation document such a plan would cost in the region of £830 million for a dual carriageway.
- Options B and C involve upgrading roads to the south of the existing route, and changing traffic priorities so as to create a manageable alternative route for local traffic. These options, although significantly cheaper, do nothing to bring the Brynglas tunnels up to EU safety standards and do nothing to address the main problem with the M4 between junctions 24 and 29: despite completion of a widening programme in 1982, there are still many places where the road fluctuates between two and three lanes.
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Traffic capacity at peak times by section
- A major consideration is that relatively high levels of traffic (40% of the total) use this short stretch of motorway for local journeys of under 20km because of the limited availability of alternative routes.
- Figures for 2008 show that the section of road approaching the eastern portal of the Brynglas Tunnel has an accident rate 65.7% higher than the average for all UK motorways, and 61.5% higher on the section of road approaching the western portal. The accident rate for junctions 26 to 25a, which includes the tunnel, is 6.5% higher than the UK motorway average.
- Traffic flow rate data also shows that the sections of M4 immediately before and after the tunnel, are operating at more than 90% of capacity at peak times, and nearly 90% in the tunnel itself. It is generally regarded that operating at 80% of capacity leads to "some operational problems" and increased likelihood of accidents, while flows above 90% lead to "severe operational problems".
- The consultation document says: "The most common accidents on the M4 between junctions 23 and 29 are rear-end shunts on both the westbound and eastbound approaches to the Brynglas tunnels. This is largely due to the stop-start conditions that occur during peak periods caused by the motorway reducing from 3 lanes to 2 lanes."
- Last year a truck caught fire inside the tunnel, causing structural damage that is still the subject of ongoing discussions between the Welsh Government and the lorry company's insurers. The public consultation period lasts until June 6.
- Truck blaze damages UK traffic tunnel - TunnelTalk, July 2011
Engineers assess damage to M4 tunnel - TunnelTalk, August 2011
Brynglas: A story of innovative solutions - TunnelTalk, November 2011
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