myCar isKindOf "LandVehicle"
You will need an array with all the other vehicles in it to use this:
({(myCar distance _x) < dist} count vehicleArray) > 0
You can make the vehicleArray in your init.sqf or you can place a trigger that covers all the vehicles in question, set it to side present once. In the On Activation:
vehicleArray = [] ; {if (_x isKindOf "LandVehicle") then {vehicleArray = vehicleArray + [_x]}} forEach thislist ; if (myCar in vehicleArray) then {vehicleArray = vehicleArray - [myCar]}