The impact of bridge strikes made headlines once again at the start of this month following a collision in Cornwall. Holidaymakers on their way home from Cornwall experienced severe delays after a Tesco lorry struck a bridge at Mannamead in Plymouth.
A bridge strike is any incident which involves a vehicle colliding with a bridge structure, this can be either underline (where a railway line passes over road) or overline (where a road passes over a railway bridge).
According to data from Network Rail, in 2019 there were 1,787 bridge strikes reported. Of these strikes, 1,686 (94%) were underline strikes, caused by overheight vehicles colliding with a bridge.
When a vehicle collides with a bridge, the consequences can be significant and far-reaching, as the vacationers in Cornwall recently discovered.
The average cost of each bridge strike is over £10,000, with the most costly single strike in 2019 amounting to £1.8 million in train delay costs, according to Network Rail.
As seen in Cornwall when the lorry took more than 24 hours to remove, a bridge strike can lead to serious disruption on the road network. Not only that, but collisions could even leave to death or serious injury of the driver or other road users.
Any collision is likely to cause significant delays regardless of the level of damage as the bridge cannot be used until it has been fully inspected following a strike.
Should a collision cause significant damage to the bridge, trains travelling on the railway are also at risk of a serious incident or even derailing.
Careless driving of overheight vehicles can lead to serious financial losses, including: the driver losing their job or driving license, increased cost to insurance policies and even loss of a company’s operator’s license.
Should a commercial vehicle strike a bridge, the company will also be liable for all costs relating to examining and repairing the bridge. Costs must also be covered for recovering the vehicle and its load, along with any costs incurred by delays to train services.
This latter liability can run into the thousands or millions and so avoiding bridge collisions is of critical importance to both those using the road network and local authorities managing it.
Drivers must know the height and width of their vehicle before starting their journey and also ensure they have checked their route for low underline bridges.
However, it is impossible to plan for every eventuality such as route diversions or road closures and therefore road signage can be critical to help avoid bridge strikes.
Overheight detection systems are a highly accurate solution capable of detecting vehicles using break beam or bi-directional technology. They can detect vehicles that have exceeded a height tolerance, without human intervention.
With an overheight detection solution, there are multiple sensing device options available including Photoelectric Gates, above-ground detection (Flir and AGD Cameras), inground detection (loops or studs) or a combination.
Photoelectric Gates use break beam technology, allowing the user to specify a pre-determined height for detection. Photoelectric Gates come in 2 options; Effective Beam, which have powered sensors set up at either side of the road at a safe point before a low bridge. The other option is retroreflective, unlike an Effective Beam sensor, this option uses a polarized reflector on one side, eliminating the requirement of power on both sides of the road, along with potentially limiting the amount of civils work required.
In order to ensure the overheight vehicle is travelling towards the bridge and not away from it, it is also possible to install a FLIR camera or use a radar to register the direction of traffic.
Another way in which to ensure the solution has correctly identified an overheight vehicle is by utilising inground detection technology like loops.
The loop can detect when a vehicle goes through it, so if the Photoelectric Gates, radar, or sensor has also been triggered, the system can initiate the illumination of signage warning drivers that their vehicle is too high. This helps avoid mistaken overheight warnings being triggered such as if a bird flies through the sensor.
Should the detectors be correctly triggered, the technology sends an alert to the Central Management System (CMS), so the user is aware there has been an over height vehicle approaching a bridge. The CMS will record that the sign has illuminated and so the driver has been warned before potentially hitting the bridge. This helps to ensure that the driver takes accountability for the incident.
TWM has installed overheight detection technology in several locations across the UK, including a project for Irish Rail. There had been several bridge strikes at one identified location on the Irish Rail network in the 12 months before installation, with significant remediation costs incurred to repair the damage after each incident.
In this situation, reactive measures were taken to avoid further incidents. However, the overheight detection technology is widely proven to be effective in preventing bridge collisions and so should they be installed proactively at potential strike locations, substantial costs can be avoided.
TWM ensure their solutions are installed in accordance with the TOPAS standard, however, we are continually striving to innovate our solutions for our customers. Our latest developments include more energy-efficient sensors with retroreflective signage that will reduce the carbon footprint of the solution. To guarantee performance, the technology is typically mains powered and so TWM seek to reduce energy consumption wherever possible in the solution innovations.
In order to capture more details of any bridge collisions, future solutions can also be expected to involve video cameras that begin recording once the sensors are triggered in case a lorry continues towards the bridge.
The sensors involved within the overheight detection technology can be set at a height to suit the application required. These applications can include bridge decks, car park height warnings, overhead power lines and overhead infrastructure which needs protecting and could be susceptible to collisions.
It is also possible to replace sensors on either side of the road with a FLIR camera in order to help with traffic flow on private sites, as was the case with the installation for Baxi UK in Preston. The cameras counted only specific types of vehicles that were entering the site that could impact traffic flow. This solution could be applied to environments such as airports and docks.