Bridge strike
Bridge-strike road accidents, in which an over-height vehicle collides with the underside of the structure, occur frequently and are a major issue worldwide.
Texas Department of Transportation estimated in 2013 that an average cost to repair a bridge strike is $180,000 USD.
These include economic impacts due to road closures, and police response and cleanup costs.
An impact of the oversize load to multiple sway braces was enough to damage load-bearing members and caused a span to be collapsed, resulting in vehicles falling down to the river with three minor injuries.
[16] In 2010, a rail bridge strike of a double-decker bus on a New York parkway killed 4 passengers.
[13] In 2022, a truck carrying liquified petroleum gas scraped the underside of a low bridge in Boksburg, South Africa, causing an explosion that killed at least 8 people.
[18] In United States, the Manual on Uniform Traffic Control Devices requires the placement of warning signs for any structure with vertical clearance less than 12 inches (30 cm) more than the legal maximum vehicle height.
[18] Similarly in Australia, advanced traffic instruction signs are used to provide clearance information of a low-clearance bridge ahead and accompanied by a detour direction.
When any parts of vehicles hit the chains, it creates noises to notify drivers so they can pay attention to the height restriction signs.
These structures are installed in front of the bridges or tunnels with the heights of the clearance to absorb the impacts of overheight vehicles.
[30] Fully integrated systems of overheight detectors and traffic lights have been used in tunnel operations for decades.
In an event that an overheight vehicle failed to stop at the inspection station, the secondary detector would trigger another alarm that would display a message at variable-message signs to lower the speed limit and eventually turned the red light to stop all traffic.
A major drawback of the photocell detectors was that they produced a lot of false alarms caused by snow and heavy rain.
[26] Modern detectors now use other technologies such as red/infrared photoelectric sensors, infrared laser beams, and ultrasonic transducer.
The lights will turn green after a short stop with an expectation that the drivers will notice the height restrictions and use an alternative route by themselves.
[34] In United Kingdom, a more advanced system that targets a specific vehicle was deployed at Blackwall Tunnel.
In Australia, a water curtain falling on all traffic lanes with a laser projection of a large stop sign in front of the Sydney Harbour Tunnel is used as the last resort to stop overheight vehicles that ignore all the warning signs and traffic lights.
[35] There are several systems that can be equipped in trucks or other commercial vehicles to provide bridge strike prevention.
[36][37] Similarly, the 11 ft 8 in (3.56 m) Norfolk Southern–Gregson Street Overpass, nicknamed "The Can Opener", in Durham, North Carolina, US, was very frequently struck by vehicles, and received international media attention[38] until it was raised in 2019.
[39] Infrared sensors, which trigger warning signs when a high vehicle approaches, were added to an underpass in Frauenfeld, Switzerland, only after several incidents.
[48] In 2014, the United States Coast Guard published statistics that it investigated 205 bridge strikes in the eleven years prior to the publication.
The primary causal factor was the lack of accurate air draft data, the distance between water surface to the top most part of the vessel.
To prevent controlled flight into terrain, tall bridges may bear aviation obstruction lighting that notifies pilots of their presence.
