You obviously don't drive a truck. The current level of inspections of US trucks is a minicule percentage of the trucks on the road. Many weigh stations are closed a large part of the time. Adding the Mexicans will just make it harder for DOT to get around to all of the trucks.
This issue is going to come to a head as US truckers figure out that the Mexicans are cutting their throats price-wise to get backhaul.
Then the shooting starts.
Most of the NAFTA traffic will be thru Texas.