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bridge markingsBridge Bashing

The phenomenon of high sided vehicles hitting low bridges is a surprisingly common occurrence, some estimates have suggested around two strikes per day in the UK on average. In addition to the dangers caused beneath the bridge, the bridge itself may have to be closed to traffic crossing it, pending structural assessment. This can be particularly costly in the case of rail-over-road bridges where line closures are required and diversions difficult to achieve.

The bridge bashing project was commissioned to investigate collisions with bridges and the issues behind such human-error with the aim of reducing bridge strikes specifically in rail-over-road bridges. It is a difficult process to judge as most drivers of high-sided vehicles sit considerably lower than the height of their vehicle, which in many cases they cannot see, making direct sight-based judgment or comparison of any mismatch between bridge and vehicle heights almost impossible. Vigilance and awareness must therefore be maintained to consciously assess the heights involved, but in a complex and/or tedious driving environment this can at times be diverted to other matters. An intrinsic awareness of vehicle height can also be lacking for other reasons, such as where vehicle height varies (e.g. due to its load or the ability to raise it's load), where drivers frequently drive to familiar destinations in lower vehicles, or where the bridge has less than optimum characteristics (such as an arch of varying height or a position that is occluded from view during the approach).

A number of experiments were carried out to investigate issues such as driver's awareness of prior warning signs and bridge markings. These included laboratory simulator trials, eye tracking and finally real-world trials with a lorry and an adjustable-height bridge. One of the key suggestions to arise from the work was the design of bridge markings which focus the mind on the concept of limited height by means of optical illusion in the bridge markings, making the bridge seem lower than it actually is.


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