This was posted to HN before. The comments on that were basically, it's been done before, and wasn't economical/safe. Keep in mind, you still have to spend ener

This was posted to HN before. The comments on that were basically, it's been done before, and wasn't economical/safe. Keep in mind, you still have to spend energy to accelerate the cars, and there are a lot of safety issues introduced by the extra complexity.