an installation at points where a railroad track crosses a highway at grade. In accordance with the general requirement that all types of railroad crossings ensure safety in railroad traffic, railroad crossings at grade are built in places where there is good visibility and usually at right angles but never less than 60° to the axis of the railroad track. The minimum width of a crossing is 4.5 m, but it must not be narrower than the width of the highway crossed.

Depending on traffic density and on the type of highway involved, railroad crossings may be classified into four categories, with each category having a particular design, signaling, gates, and lighting. Depending on traffic density, visibility and the use of automatic devices, railroad crossings may be guarded or unguarded. An apron is laid at the crossings, and its approaches are guarded by posts or railings and by warning signs. In order that the rail circuits not be activated when motor vehicles are crossing, the apron between the rails is made 30 to 40 mm higher than the tops of the rails. On electrified lines, special clearance gauges are installed on both sides of the track to limit the height of freight being hauled (not over 4.5 m).