Features:

Rail bridges allow rail crossings without signals.
3 bridge types for straight and diagonal crossings.
Research Logistics 3 to unlock rail bridges.
Bridges cannot build on top of rails, mine the rails first.

Known issues:

A train going over and under a bridge at the same time will collide with itself.
Trains always render on top of rail bridges.
/editor instant deconstruction does not work on rail bridges. (72215)