When we had our new sewer system put in several dump trucks trucks drove over the 4" pvc downspout drain lines that were buried at least 24" below the surface in heavy clay soil. They completely flattened both lines they drove over. and I had to replace them. I would suspect that if you drive over the lines a lot you could have the same problem even with a smaller vehicle. It may depend heavily, no pun intended, on how much weight, how often, how deep the lines are and the type of soil.