TL;DR
Introduce the ability to drive the car on train tracks via research.What ?
Here is real world example of a road vehicle that has been modified with the ability to drive on rails.If you're currently on top of the rail (and traveling say +/- 5 degrees of the track direction) and press a particular hot key, it will toggle rail travel, allowing you to go only forward and backwards along the rail without turning, until you disengage by pressing the hot key again.
As the driver you operate the car manually, however your car will count as a vehicle on the track as far as train signals are concerned.


