James Fisher Strainstall (JF Strainstall), contracted by London Underground on behalf of Transport for London, installed a collision detection system, Bridgestrike, on two bridges in London; Loughton and Fairflop.


After the success of a previous installation at Watford for London Underground, where 30 strikes were recorded over an 18-month period, JF Strainstall were approached to install Bridgestrike at the two new locations.



The bridges were prone to being hit by large vehicles, despite warnings designed to deter vehicles that were too tall from attempting to pass.

London Underground were seeking a cost-effective solution that would enable them to monitor any strikes to their assets and record the offending vehicle(s).



JF Strainstall offered a comprehensive solution encompassing a hardware and software package to identify where and when there had been a strike on the bridges, additionally capturing the collision data (such as accelerations) along with vehicle identification.

Six accelerometers in total were set up on each of the bridges (four on sacrificial beams either side of the bridge, two on the structure itself). Additionally, two cameras were installed at optimal vantage points to record any offending vehicles in the event of a collision.

When a strike is recorded, an automated response is triggered and a report is sent to the client enabling quick analysis and response to any potential fault in structural integrity.


There are over 2,000 collisions to bridges in the UK every year causing severe disruption, road closures and rail lines being shut down leading to significant costs, delays and congestion.  As a result, Network Rail estimates that bridge strikes cost around £23m in repairs, compensation and delays annually.

I have found the Bridgestrike system to be an effective and fantastic tool for immediately notifying me of a bridge strike. It has allowed me to act as soon as a strike takes place, meaning structural integrity can be assessed and any repair works undertaken without delay. Since its installation in 2016, the system recorded more than 30 bridge strikes, with the system allowing us to identify offending vehicles and pursue drivers for the cost of any damage.

Transport of London
JF Strainstall
Registered office: Fisher House, PO Box 4, Barrow-in-Furness, Cumbria, LA14 1HR, UK Registered in England no. 4042929 E: enquiries@jf-strainstall.com