This sticky note puppet shows an idea that at first seems really dangerous and stupid. Which is why it's worth giving it a second thought.
A train goes from A, stops at B, goes to C.
First the usual way, then a different way.
If 10% of the train wants to stop, do you have to stop the whole train? Can you keep the train moving and load/offload passengers "on the fly."
Bullet train have proved to be very efficient in other parts of the world and will probably become a very important form of transportation over the next 50 years. Locally, California has already approved funding to build a bullet train from LA to SF. (Let's get on it Gobernator!) If ridership someday reaches enough critical mass, this general concept could be a practical way to save time and fuel.
The bullet train would exchange passengers through a detachable car that docks in the rear. The exchange car undocks, decelerates and gets side-tracked to the station. A different exchange car at the station accelerates, gets tracked onto the main line and approaches the bullet train to dock behind it. The exchange car would have its brakes synchronize to the train's brakes with a radio signal. The brakes default to "stop" in the case of signal loss. Once the exchange car is docked, the exchange of passengers between cars is as safe as traveling between any other cars on a train. A double door can be used to insure no passengers get caught between cars during detachment. When you split up the details of the problem, it starts to seem pretty safe. Who knows, maybe they're already doing it in Japan.