2350 is just the length of the cars one next to each other without factoring in any distance you obviously need to have between each car for safety.

Stopping distance at 40mph is apparently around 20m (without human reaction time)

With reaction time included is about double. So you need at least another extra 40m between each car.

There’s 499 gaps between those 500 cars so that gives you an extra 20km.

So your “train” of Model Y need roughly 23.5km worth of tunnel to move 2000 people.

Doesn’t look very efficient if you ask me.