For a game in the not too distant future or maybe for the 2300AD. The Baltic Loop is a vactrain that can travel at supersonic speeds.
The distance between the stations are only 2-3 minutes. The train runs in both directions. 4 trains runs in each direction. This means that a new train arrives at the station every 9 minutes.
Adventure hooks:
The Island Games is held on Gotland, Åland and Saaremaa. The participants from many other island arrive by air in Helsinki or Stockholm. Now the PCs must help one confused team to go to the correct island using the Baltic loop.
The Baltic Loop is closed down one day to try to set a speed record (and beat the Californian HyperLoop). Agents from the Californian HyperLoop tries to sabotage the record attempt. The PCs must help with the record attempt and stop the Californian agents.
Courland has just become an independent nation. The Latvian flag has to be replaced on every sign at the loop. Latvian agents are trying to sabotage this. Polish agents turn the Courland flags upside down to make them look like the Polish flag. The PCs must stop the Latvian and Polish agents.