The primary cause of why you're seeing roaches inside your car, is the presence of food. Even tiny crumbs are enough to become a reliable food source for those roaches. If you typically like to eat inside your car, either curb this habit. Or, practice more diligent cleaning after you're done eating, to ensure that not a single crumb is left in your car. Otherwise, roach infestations also occur rather frequently in work vehicles. For example, a builder's truck or van may contain leftover traces of mulch, firewood and recycling materials. These too could attract roaches to from a nest inside your car. Therefore, vacuuming up and cleaning your interior is crucial with getting rid of a roach infestation inside your car.