Collision damage is mainly caused by accidental vehicular impact, which often results in damage to bridge parapets and can, in certain circumstances, have disastrous consequences. Many older bridges have substandard road widths and alignments, both horizontally and vertically. Excessive vehicle speed is also often a factor in parapets being struck.
Where damage is caused to other property, such as a bridge parapet, this is a reportable collision under Section 170 of the Road Traffic Act 1988 as amended by the Road Traffic Act 1991. Once a report is received, Northamptonshire County Council will always try and recover the cost of the repairs via the vehicle owner's motor insurance. However, in some rare cases the repairs have to be funded from our limited bridge maintenance budgets.
Northamptonshire has nearly 2000 highway bridges - some new, others centuries old - and often our older structures can be 'Listed buildings' or even 'Scheduled Ancient Monuments', for which formal consents are normally required when any works are undertaken. All works need to be treated in sympathy with the bridge environment. We try to maintain these efficiently with the minimum of disruption.
Many older structures on the network are not designed to current standards. For example, they may have reduced height and a lower level of vehicle containment. It is only on the most modern bridges that parapets will comply with today's design standards.
Parapets are protective devices that are designed to reduce the severity of an accident when a vehicle leaves the carriageway. They provide a passive line of defence. In addition, the parapet may be required to protect the area below the bridge.
In some cases the damage is significant with the vehicle ending up in the area below the bridge, this could be another road, a river or even a railway.
The county council has a duty not only to safeguard members of the public but to manage our structures so that they do not pose an unacceptable risk to public safety. When a bridge parapet is significantly damaged or even totally demolished, urgent action is required to put interim arrangements in place to protect the safety of the travelling public.
Where repairs cannot be immediately undertaken, then interim arrangements will be used such as traffic management, temporary concrete safety barriers and fencing to prevent further collisions. Road closures are used as a 'last resort' where there is no suitable, safe alternative, traffic management as we recognise the disruption these create.
We monitor where bridge strikes occur and if we identify a particular pattern of frequent damage then a wider review of the area will be undertaken to look at preventative interventions.