It's actually quite expensive (almost all of which is being paid by the railroads and not the government), which is why the mandated date for railroads to complete their PTC (Positive Train Control) systems have been extended twice.

Even with PTC in place however, what happened in Hoboken would not have been part of the system since PTC is primarily to keep two trains from running into each other and to ensure they don't speed around curves.

Some European and other countries already have a system at terminals that in fact do apply the brakes of a passenger train, if the sensors determine that it is going too fast and won't be able to stop before it hits the bumper blocks.

The recent incident is a real tragedy that could have been prevented, but it also must be recognized that this kind of accident is very rare for passenger and commuter trains.