are they the full time staff going into work? or are they retained rushing to park and get out on a call?
are they parking across your drive or just parking on road and you cant manoever out?
i would suggest a call to the officer in charge of the station, either the full time or retained, depending on who is parking there,.
sometimes when in cases of emergency, time looking for parking could be costing lives but as you dont say under what curcumstances its occuring no-one knows if thats the case here