Colwall Bridge progress report 2

Colwall Green Railway Bridge was closed to traffic following an inspection by Owen Williams, the council's engineering consultants, on Saturday / Sunday 11/12 August. The decision was made on the grounds of public safety because the inspector had serious concerns as to the capacity of the bridge.

The report from Owen Williams was the best information available at that date on the capacity of the bridge but data was incomplete and this gave rise to uncertainties as to the bridge's strength. To open the bridge would put the public's safety in jeopardy.

Progress up date

The bridge was inspected again over the nights of 14/15, 15/16, and 16/17 October. This inspection was a major step in the progress towards re-opening the bridge to traffic.

Working within touching distance of the structure all visible elements of the bridge were comprehensively inspected by two engineers. The inspection included the following work:

• Measurement, recording and photographing of all defects (based upon extent, severity and location).
• Measurement and recording of all section sizes and spans.
• Bricks were removed at two locations (the arches supporting the road) to determine the condition of the hidden parts of the cross girders.
• Levels were taken on the bridge soffit and transversely and longitudinally across the carriageway.

The results of the assessment using the inspection data will be complete at the end of the year. The assessment process is detailed and complex. It must accurately assess all aspects of the bridge's strength taking into account the different elements and varying degrees of deterioration. The method of analysis is a two dimensional computer model known as grillage analysis.

The council is continuing with its two-option strategy - inspection to determine the capacity of the bridge and consideration of installing a bailey bridge. The design of the proposed temporary bailey bridge over the existing bridge has been submitted to Network Rail for approval. This will be processed through Network Rail as quickly as possible.

Network Rail will rigorously assess how the proposed bailey bridge affects the existing bridge. It is important therefore that the design of any temporary structure clearly demonstrates that there will be no adverse affect on the existing bridge. This will aid the prompt acceptance of the proposals.

The strength of the structure

The inspection just completed and the assessment will determine what load the bridge can take. Collating and assessing the data from the inspection will be time consuming because of the need for completeness and accuracy. However this time spent at the beginning will ensure that the results are accurate and any opening to traffic will be safe.

If there is any opportunity for light traffic to safely use the bridge, as an interim measure, that opportunity will be taken. It is too early to give the likelihood of this being a safe option.

All the data from the inspection will also be given to Network Rail in order that they may carry out their own assessment of the bridge's capacity.

Herefordshire Council and Network Rail both await the results of the assessment in order they may accurately determine the capacity of the bridge.

The engineer's report (titled Early Notification Report) that brought about the bridge closure in August can be viewed through the parish council.

Has any increase in the size of vehicles using the road contributed to the condition of the bridge?

The size of vehicles allowed to use the highway is a national matter, not one that can be determined locally. We are obliged to assess our bridge stock against these national standards and take action to upgrade / maintain the structures where necessary.

Diversion signage

We have installed over eighty signs marked with symbols to direct traffic along the diversion routes. The use of symbols rather than place names is the most appropriate because their size allows them to be installed more easily (few site restrictions), they do not noticeably increase roadside clutter and are more versatile if the route is changed.

Diversion routes

It is appreciated that the road categories for the signed diversion routes are not ideal. Much of the traffic is local and typically drivers adjust their journey to suit their circumstances. However there is the potential for inappropriate traffic use of the routes and so this is kept under review. Where instances of inappropriate use is brought to the attention of the council these are investigated and resolved as best as possible.

The impact of increased vehicular traffic on the diversion routes has been noted. There have been significant improvements on the routes through, for example, ensuring that signs are clearly visible. The council shall, of course, continue to monitor the conditions of these routes and intervene with maintenance measures as necessary.

The inspection frequency on the diversion routes has been raised to monthly and repairs actioned as necessary. This is the highest frequency of inspection that we normally operate. When the diversion route is removed the condition of the route will be assessed to ensure that any outstanding damage is rectified.

The diversion routes have been included on our primary winter gritting routes.

Effects of the closure

The council appreciates that the closure can cause isolation for some members of the community and is appreciative of the concerns raised by businesses relating to lose of trade. The council is therefore working with Network Rail and Owen Williams to minimise the affect and duration of the closure.

Legal issues

Owen Williams, as a competent consultant, has advised Herefordshire Council that the condition of the bridge, on current information, gives cause for concern in respect of public safety. The view of a third party does not relieve the council of its responsibilities for acting on that advice.

The extent of the difficulties that the closure of Colwall Green Railway Bridge has caused is very much appreciated and is at the front of our thoughts when organising the investigations and subsequent work. Herefordshire Council is making every effort, in conjunction with Network Rail, to return the bridge to service as quickly as possible.

Progress reports - If you wish to receive forthcoming progress reports direct by e-mail please contact the council through the routes given below.

For further information please contact Herefordshire Council, Highways and Transportation, Unit 3 Thorn Business Park, Rotherwas, Hereford, HR2 6JT, Telephone 01432 261800, email streets@herefordshire.gov.uk

This sheet can also be obtained from the Colwall Parish Council website http://www.colwall.net/