overbridge

Noun

 * 1)  A bridge that allows traffic to pass over a road, river, railway etc.

Usage notes
Where a bridge takes one form of transport over another it is both an overbridge and an underbridge, 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.

Verb

 * 1)  To form a bridge over; to overarch.