It's been over a decade and I didn't drive while we were there but I remember it looking a lot like a tollbooth in the US, but one with military/police looking people that would randomly, or not so randomly, select people to pull off to the side so that they could search your vehicle. At least one time when we crossed into France to go grocery shopping we were searched and had to show our passports and they looked through our groceries and asked to see the receipt.