Road–rail bridges are bridges shared by road and rail lines. Road and rail may be segregated so that trains may operate at the same time as cars (e.g., the Sydney Harbour Bridge). The rail track can be above the roadway or vice versa with truss bridges. Road and rail may share the same carriageway so that road traffic must stop when the trains operate (like a level crossing), or operate together like a tram in a street (street running). Road–rail bridges are sometimes called combined bridges.