Thinking of this setup you have one big problem: train is just very long linear corridor. That forces your maps or environment into quite boring layouts.
As for collision problem, if this game is not multiplayer, you can avoid whole collision problem by realizing that movement is relative. You can load each car as streamed level.
Car that player currently is in can be stationary, with next and previous car simulating bending. Then you add some moving skybox outside for some cars.
To get that feeling of real train bending on track you can use scaled down spline and just read locations 3 cars ahead and behind, then calculate rotations.
But imo biggest challenge here is making environment that not only looks nice, but is also fun and not repetitive.
GL with project.