SL Rail & Cable Monorail/Trains use a passive track. The "engine" is automated from a central controller (on start) and knows only when to stop at a station, when to start slowing down and how long to wait at each stop. Like a 'real' train it goes where it goes because that is where the rail goes. There is no sensing, individual track part naming, etc etc etc.
Havok 4's prim seam error has borked the smaller Monorail tracks but the larger trains (as used in several subways in SL) are working fine after some adjustments to braking distances and weight required by H4 changes. The use of glass as a material worked fine prior to H4 but since then it has created a sort of variable friction - something (maybe lag) affects it. Returning to wood as a material seemed to fix that.