Very basic LEGO train control with Arduino
To command up to 4 train track without modify anything. No electronics on trains.
Uses an infrared proximity sensor to detect train near a station and stop it. Then wait two minutes (configurable in the Arduino source) before start train again.
Each track is controlled with its own sensor and relay.
Electronic parts are cheap and easily available on Amazon.
NB: use gEDA (http://www.geda-project.org/) to open schematic.