Structure gauge

The structure gauge, also called the minimum clearance outline, is the minimum height and width of tunnels and bridges as well as the minimum height and width of the doors that allow a rail siding access into a warehouse. In addition, the term may apply to the minimum distance to railway platforms (passenger or freight), buildings, electrical equipment boxes, railway signal equipment, third rails or to supports for overhead lines from the track. The width of a narrow cut can also affect the maximum loading gauge.
The difference between the structure gauge and the loading gauge is called the "clearance". The amount of clearance between the loading gauge and the structure gauge depends on the speed of the train, due to the train wobbling, so a train may be able to get past a restricted clearance by travelling at slow speed.
Road traffic application.
The term can also be applied to the minimum size of road tunnels, the space beneath overpasses and the space within the superstructure of bridges, as well as doors into automobile repair shops, bus garages, filling stations, residential garages, multi-storey car parks and warehouses.
Accidents.
A high overpass bridge near St Petersburg is known as the "Bridge of Stupidity" because it is often struck by vehicles despite many warning signs. In May 2018, after it was struck for the 150th time by a GAZelle truck, a birthday cake was presented to the bridge. This made national news.
Similarly, a overpass in Durham, North Carolina, USA, was frequently struck by vehicles, and made the news a number of times until it was raised in 2019.
Infrared sensors which trigger warning signs when a high vehicle approaches were added to an underpass in Frauenfeld, Switzerland only after several incidents.
A similar situation exists at an underpass on Guy Street in Montreal.
Another problem is the Montague Street Bridge in South Melbourne