That's part of the game: competition... you just have to be better than the computer
Scatty is right, get a smaller number of wagons for each train to decrease the waiting time, and get more trains assigned to each station (you can run a single line station with two trains quite easily, you just have to provide a few "crossings" - don't forget to place some light rulers); this way, you can have one train loading while the other is making the trip and when the first train is loaded, the second is about to arrive empty.
There is another way to turn around this - it's not a pretty one (in fact it's quite dirty
) but it works: when your opponent is building his railroad network between his stations, place a few diagonal railroad ahead of his way to block him the passage. He'll spend most of his cash trying to go around, building bridges, tunnels and modifying the terrain until he'll be broke :amused: