I have yet to visit an MTB centre that has height restrictions at the entrance to the car park (Gisburn, Llandegla, Cwmcarn, Sherwood Pines, Clayton Vale (M/cr), Phillips Park (Prestwich), Cannock Chase). Given the intended users of the car park and the likelihood of roofracks and day vans (the number of fancy VW T5 vans in the carparks is astonishing). It would be a pish-poor design flaw if height barriers were installed and one could argue almost negligent of the facility providers.
Having said that, if you think you have such poor awareness of the conditions around you as you drive are you sure you should actually be driving?