Near where I live we've got a guided busway (a track system that modified buses can travel down, tram-style). On the railway bridge before it's entrance there'

Near where I live we've got a guided busway (a track system that modified buses can travel down, tram-style). On the railway bridge before it's entrance there's a height barrier in advance consisting of a whole load of bells that dangle down from a metal bar and will hit over-height vehicles without making a really solid collision. They still haven't figured out a way to stop cars driving up the bus tracks, though (where they inevitably get stuck).