I suggest in the game that when a fire station is sent on a mission and the station is empty of an operational vehicle, an operational vehicle can be deployed from the nearest station to the station to clear that area. Cover.
If possible, tell the game developer to do so in future updates
Basically you are asking for vehicles to be sent on stand by at stations where their units are on larger calls.
This has been suggested before and is being looked at but don't think it will happen as don't think it will be practical bit like patrol routes.