I think a REALLY fun way would be to use magnets like said.
Line under the tracks a bunch of small electromagnets, and keep one on the bottom of each car, and as the magnets pass each other, the electro switches polarity to either push or pull the car. With the right force, each car would end up rolling at the same, safe speed. All the switches could be operated by computer, and you have a yard operator select what track the car goes to, and the computer sets the switches for you.
Obviously extremely expensive, and very large. But would make for one heck of a show piece.
Line under the tracks a bunch of small electromagnets, and keep one on the bottom of each car, and as the magnets pass each other, the electro switches polarity to either push or pull the car. With the right force, each car would end up rolling at the same, safe speed. All the switches could be operated by computer, and you have a yard operator select what track the car goes to, and the computer sets the switches for you.
Obviously extremely expensive, and very large. But would make for one heck of a show piece.