Railways operate in a variety of terrains and environments. There are a number of engineering methods deployed to assist successful train operation in these environments.

Trains prefer operating on flat or level surfaces as they have a maximum grade at which they can climb or descend. Train tracks are commonly sited on top of ballast to allow rainwater (and minor flooding) to drain away without affecting track alignment. ballast is also a particular shape to lock together and prevent rail and sleeper movement. The ballast may be on an embankment which is a raised level across mildly undulating terrain or low-lying wet areas.

Where faced with a hill, the route designers may choose (in ascending cost) to go gently around it, dig a culvert (ditch) or tunnel though it to maintain track within the maximum grade. In some major cities, entire systems are in tunnels.

Where faced with a valley, the route designers may choose (in ascending cost) to gently go around it, cut and fill the tops of peaks into the gully, build a bridge it or construct a viaduct. In some major cities, entire systems run on viaducts above roadways.