Solution to the problem of traffic congestion around Newport

Transcription

1 OBJ6917 I object to the proposed construction of a motorway to the south of Newport and provide an alternative solution for the inspectors' consideration in the attached document. Benjamin Potts-Johnson Solution to the problem of traffic congestion around Newport A commonly held assumption is that the traffic congestion around the Brynglas tunnels is due to the tunnels being physically limited to two lanes in either direction. It is worth noting however that a few miles along the M4, junction 24 (Coldra) is also restricted two lanes in either direction, as shown below. As the traffic data indicates ( M4 traffic flow through junction 24 is comparable to the traffic flow through the Brynglas tunnels. The two lane restriction of junction 24 does not cause traffic congestion. Traffic congestion is only experienced at junction 24 when it is backed up from the Brynglas tunnels. The two lane restriction of the Brynglas tunnels is therefore not the cause of the traffic congestion that is regularly experienced, as is commonly assumed. The primary causes of traffic congestion at the Brynglas tunnels are: 1. inadequate lighting in the tunnels, 2. the close proximity of junctions 25 to 28, and 3. local traffic using the motorway for short stretches.

2 Secondary causes of traffic congestion includes vehicles using the filter lane to pass traffic on the left then re-joining, and changes is speed limit; both due to congestion. Resolving the primary causes of congestion will naturally resolve the secondary causes. Tunnel lighting The lighting system within the Brynglas tunnels has not been properly maintained for many years and this failure is the primary cause of traffic congestion at the entrances to the tunnels. The entrances to the tunnels are dimly lit at all times of day and night and although some work has been done on the lighting system recently, it is insufficient to resolve the problem. It is worth noting that traffic congestion in immediate proximity to the tunnels is worse on sunny afternoons. Below is a picture of the entrance to the Westbound tunnel on such a sunny afternoon. The problem is clearly one of poor lighting. Drivers entering the tunnel from bright light conditions to low light conditions experience momentary disorientation as their eyes adjust to the dark. Due to this disorientation, many drivers will hesitate and break slightly as they can t clearly see what is ahead of them. In heavy traffic flow conditions, a slight slowing of one vehicle has a knock-back effect which eventually results in slow moving traffic. This effect is well understood. The solution to the problem is clearly proper lighting. The tunnels must not just be well lit, they must be lit in proportion to the ambient light conditions i e the tunnels must be brightly lit on bright sunny days and less well lit at nightime. This might seem counterintuitive, but the object is to minimise the difference in light levels inside and outside the tunnel to avoid the need for drivers eyes to adapt to changing

3 conditions, and the problem this causes. Adaptive tunnel lighting is well understood in the industry although is not currently widely utilised in the UK. As the power requirement for adaptive lighting inside the tunnels is proportional to the ambient light level, part-powering by solar panels is logical. Local traffic and junction proximity The local M4 was in part built as a bypass for Newport. The close proximity of junctions makes the M4 useful for local journeys. A large proportion of traffic on the M4 is local traffic which joins at one Newport junction and exits at another Newport junction and only uses the motorway for a few miles. Vehicles joining a motorway always disrupt the smooth traffic flow in heavy traffic flow conditions and increase the risk of congestion occurring. In addition to this effect, it is commonly observed that vehicles using the motorway for short/local journeys travel more slowly than through traffic. It is not uncommon for vehicles using the motorway for local journeys to be travelling at 50mph and occasionally 40mph when conditions are otherwise good. The difference of speed in these flows of traffic is another cause of increased risk of congestion. The first solution is to use lane 1 as a continuous filter lane for multiple junctions between junctions 24 and 28 westbound and between junctions 29 and the tunnel eastbound. Through traffic will be directed to use lanes 2 and 3 for several junctions before the tunnels, creating a stabilised flow of two lane traffic ready to pass through the tunnels smoothly and efficiently with minimal disruption from junctions. With proper management, a flow rate of 7200 vehicles per hour in each direction through the tunnels is achievable. This is more than sufficient for current demand. The second solution is to create alternatives for local traffic. Much of this local traffic is from the Ebbw valley: Rogerstone, Bassaleg and further afield. A rail line already serves the Ebbw valley all the way up to Ebbw Vale. This line passes through Newport on the way to Cardiff but doesn't stop in Newport. This is because the line does not pass through Newport's main rail station, making it of no use to commuters travelling into and out of Newport. A new station on the existing line at Ebbw Junction on the site of the Bideford Road depot would draw significant volumes of local traffic away from the motorway. Increased passenger volumes on this rail line is also likely to make viable the redoubling on the line, further drawing traffic off the roads and further reducing congestion. A new station would contribute to the viability of the re-laying of track between Pye Corner and Caerphilly as part of the South Wales Metro plan. This development would have a wider effect by reducing traffic on the M4 between Cardiff and Newport as well as on local roads. The South Wales Metro will contribute to sustainable transportation and every pound spent on an unnecessary new motorway makes the metro less likely to be built. All proposals in this document will cost less than the alleged 1.1bn cost of the proposed new motorway. A final cost of 1.5 to 2bn is more realistic for the proposed new motorway. Such expenditure would further

4 jeopardise the development of an integrated and sustainable transportation infrastructure. Speed limits Variable speed limits are of limited use in resolving traffic congestion. In congestion conditions, the traffic flow speed is always less than the indicated speed limit, making variable speed limits irrelevant. Variable speed limits are used reactively when congestion has already occurred. Reduced limits are not used preventatively in an effective way. Only a permanent reduced speed limit is effective at contributing to preventing congestion. Variable speed limits can themselves contribute to congestion in certain conditions. Where a speed limit reduces, some drivers will slow down more readily than others. A driver reluctant to slow down behind a driver complying with the changed speed limit may get very close to the vehicle in front. Insufficient spacing not only increases the risk of accidents but also increases the risk of traffic congestion due to late braking and the knock-back effect that can cause. Also, some drivers are also more observant than others. Many drivers do not notice a changed speed limit for some time, particularly when their attention is focussed on other vehicles in heavy traffic conditions. The speed limit should therefore not change in a congested stretch of the motorway. The solution is to set a single permanent speed limit for the whole stretch of the motorway around Newport. The ideal speed limit depends on a number of factors. The eastbound carriageway from junction 28 to junction 27 narrows, rises and curves to the left. Traffic joining at junction 27 suddenly appears to eastbound traffic due to the tight geometry of the slip roads. These conditions lead to sudden lane changing, disrupting the flow of traffic and consequently congestion. The normal 70mph speed limit is too high for this stretch of the motorway as time to react to changing conditions is limited. The single speed limit must therefore be less than 70mph. Spacing between vehicles depends on the speed the traffic is flowing at. Reducing the speed limit reduces spacing between vehicles so when vehicles join the flow of traffic at a junction, they cause more disruption to the flow of traffic if the spaces they enter between vehicles is less. This disruption to the flow of traffic increases the risk of congestion conditions forming. Speed limits set too low can therefore contribute to congestion. This effect can be seen on the M4 at Port Talbot since the enforcement of the 50mph limit by average speed cameras. A speed limit of 50 mph is therefore too low. The optimum speed limit is a permanent and continuous 60mph limit in both directions between junctions 24 and 29. Summary

5 In summary, the solutions to the congestion problems on the M4 around Newport are: 1. installing adaptive lighting in the Brynglas tunnels; 2. creating a continuous filter lane in both directions between junctions 24 and 29; 3. setting a single continuous and permanent speed limit of 60mph in both directions between junctions 24 and 29; 4. close the entry slip road at junction 26 eastbound to all but emergency vehicles; 5. construction of a new rail station at Ebbw Junction, Newport; and 6. reconstructing the rail line between Pye Corner and Caerphilly. Solutions 1 to 4 together will cost approximately 10M about 1% of the alleged cost of a new motorway to the south of Newport and resolve the congestion problem in the short term. Infrastructure investment can then be directed to the South Wales Metro proposal which at a total cost of 600M will include solutions 4 and 5 along with more widespread developments. This proposal provides much greater economic and environmental benefits than the proposed motorway to the south of Newport, at substantially less cost.