Depending on how old your previous version was, it might not have had support for half heights, which were implemented after version 120 came out. In the new version, there are two steepnesses of slopes. The clearance required to build a bridge over another way is 2, but a bridge is only 1 high. Try an experiment. Lay a line of track, then raise one square of land on either side of this track. Try and build a bridge between those two raised squares of land. It should work because the raised square is 1 high and so is the bridge, giving you the required clearance to build over the track.