Clearance (civil engineering)
In civil engineering, clearance refers to the difference between the loading gauge and the structure gauge in the case of railroad cars or trams, or the difference between the size of any vehicle and the width/height of doors, the width/height of an overpass or the diameter of a tunnel as well as the air draft under a bridge, the width of a lock or diameter of a tunnel in the case of watercraft.
[1] In roadways, vertical clearance is the measurement from the ground or the road pavement to the bottom of overpasses or bridges.
Other overpasses were left to be reconstructed to the new minimum vertical clearance at later times.
[4] Eurocode 1: Actions on structures has a definition of "physical clearance" between roadway surface and the underside of bridge element.
[6] In South Africa and the southern region of Africa, the minimum vertical clearance of modern bridges is 5 metres (16 ft 5 in), although the legal height limit of road vehicles is still at 4.3 metres (14 ft 1 in).
[7] United Kingdoms has a standard on minimum clearance of a public highway at 16 feet 6 inches (5.03 m).
These may involve over-height vehicles, or low vertical clearance bridges or tunnels.
In United Kingdom, railway bridge strikes happen on an average of once every four and half hours with total of 1789 times in 2019.
Texas Department of Transportation estimated in 2013 that an average cost to repair a bridge strike is US$180,000.
[11][12] Similarly, an 11 ft 8 in (3.56 m) overpass in Durham, North Carolina, US, was frequently struck by vehicles, and made the news a number of times until it was raised in 2019.
[13] Infrared sensors, which trigger warning signs when a high vehicle approaches, were added to an underpass in Frauenfeld, Switzerland, only after several incidents.
[14][15] A similar situation exists at an underpass on Guy Street in Montreal, which has a clearance of 3.75 m (12 ft 4 in).
This is the space from the edge of the roadway that is clear from vertical obstructions such as sign posts, utility poles, and fire hydrants.
The horizontal clearance are to prevent overhung elements such as side mirrors of large vehicles driven at the extreme edge of the roads to hit such objects.
[21] For roadways that require passing under some structures such as tunnels, there are standards on the entire width of the roads known as horizontal curb-to-curb and wall-to-wall clearances.
