Try removing the track section where the car stops, and see whether it runs on the rest of the track.
If it does, replace the section with a good spare, or check for dents/junk in the groove/bad connections etc.
If it doesn't run on the rest of the track, push it along until it does - and pull out the section at that end as well.
Your meter prods may be reading a good voltage but bits of braid in the slot might be shorting when the blade hits them, also changes in level may be lifting the braids off the rails. Try running the car in darkness - do you see any sparking? Is this a problem with just one car/one lane or all of them (check them all!).
Extreme test - run another car a little behind the first - if it stops at the same time, it's probably a short circuit. If it comes along and stalls at the same place, it should be a bad connection.
Best of luck -