How to measure object velocity?

[Opel Manta 400]

Is it possible to measure an object's speed/velocity? I have a scene containing some cars animated along curves, and it'd be super useful if there were a way to measure each car's speed in real time.

An answer here[blender.stackexchange.com] has a manual workaround, but having to do that for each frame doesn't seem very helpful. Is there an automatic solution that would perform this for each frame?