underbridge (plural underbridges)
- (Britain) A bridge that allows traffic to pass under a road, river, railway etc.
- The underneath of a bridge.
Where a bridge takes one form of transport over another it is both an underbridge and an overbridge, depending on the reference level. For example, where a road passes above a railway, the bridge is an overbridge from the point of view of the railway, and an underbridge from the point of view of the road.