ALL RADIO SIGNALS ARE LINE OF SITE, REGARDLESS OF FREQUENCY BAND!!!!!!!!!!!!!!
In the case of your car's radio, there is so much power being transmitted by the radio station(100,000 watts minimum), that it still gets reception when traveling behind obstacles. You R/C transmitter, on the other hand, only kicks out .5 watts.The signal can't force it's way around obstacles and, therefore, anything getting in the way will cause problems