Game description from the publisher:

In the dice-rolling race game Railways Express, 2-4 players travel around the USA and through parts of southern Canada and northern Mexico, building track as in the related Railways of the World game series from their individual starting city across plains, waterways and mountains based upon what they roll on the two terrain dice and two track dice.

By linking cities with track, you are awarded re-roll cubes (and possibly cards), which gives strategic options for the routes available to you as you try to connect more cities. If you're the first player to link all four cities of your color, you win!