I've sometimes discussed the optimal use of main-line railways with American friends, and put across the concept of trains with different stopping patterns sharing the same tracks.

The one which used to work nicely was on the Midland Main Line, running north from London St. Pancras. The pattern was that a semi-fast train would leave for Nottingham (180 km) and call at principal stations to Leicester (160 km). At Leicester, it would wait a few minutes for the following train (going to Sheffield, 270 km from London, via Derby, 200 km from London). This ran non-stop from St. Pancras to Leicester and then stopped at the adjacent platform to the Nottingham train.

Passengers from intermediate stations going to Sheffield could make a simple cross-platform interchange at Leicester. Passengers wanting a fast service from London to Nottingham could catch the non-stop train to Leicester then cross the platform to the train which had left London before theirs. The service was pretty optimal for all concerned.

A similar concept is used today by Eurostar. Their big constraint is the Channel Tunnel: their optimal speed is higher than that of Eurotunnel's shuttles so it's best to run the Eurostar trains close together - a technique known as flighting.

At 10:57, a Brussels train leaves St. Pancras. Just over 15 minutes later it stops at Ebbsfleet for passengers from south-east London. While it's standing in the station it is overtaken by the 11:00 non-stop train from St. Pancras to Paris. The two trains then travel some 3 minutes apart through Kent and the Channel Tunnel to Lille, where the Brussels and Paris routes separate.

A very nice use of scarce infrastructure!