I set the force to 95000 and it seems to stay on the track but it does this jitter. CLIP. Now its getting stuck again LOL. And now its flipping the cart again what the heck CLIP.
For flipping the cart, I would try to make the base part anchored and unanchor it after somone takes a seat, maybe even with a small delay inbetween sitting and unanchoring.
And I would try turning massless back off although I have no idea if that would fix any of the issues.