I have no particular experience with hairpin coasters, but for some rides you either need a station that is long enough to house more trains, or you should make use of block brakes (having 3 blockbrakes allows for 2 trains, having 4 block brakes allows for 3 trains, etc.; the station itself aslo functions as a block brake)
Emergo
The station already was 5 blocks, so I left it that way, but I added 2x Block Brakes, now I got 3 trains.. which should be enough.

