Rail-based transportation has an inescapable problem: in a single-track situation, there is no way for a train to pull over and let another train pass.
Thus, a single stopped train can block an entire track indefinitely. And a slow train can’t be overtaken by an express train.
This can be solved by adding multiple rails, but that is prohibitively expensive except in very small sections of track. Additionally, it increases recurring maintenance costs.
There is one incredibly simple solution to this problem: just put an additional set of tracks on top of every train car (Figure 1).
Now, a slowed or stopped train can be passed by simply driving the passing train over the stopped train (Figure 2).
As seen in the illustration above, this will definitely work on train cars weighing hundreds of thousands of pounds, so construction on this project can begin immediately without further testing.
PROS: Effectively turns every single track into a double track.
CONS: May cause complications if this method is employed while the being-passed train enters a tunnel during the passing process.