For some reason the current US administration was hell bent on opening up the border for Mexican trucks.
There are a number of reasons. NAFTA said it was to be done a long time ago. When the US balked Mexico did something with embargoes or tariffs or whatever so it would cost more for US products to be shipped and sold in Mexico - agriculture in particular. So there was/is/has been pressure from various groups to get this sorted out and taken care of. The US wants Mexico to buy US goods and Mexico wants the US to buy Mexican goods. But the teamsters and others do not want Mexican trucks in the US - which is costing billions in trade. So the administration was "hell bent" to get NAFTA working as it was supposed to be working for a very long time and to get those billions in trade moving into our economy. Yes, it is complicated and probably not something that can be completely explained on this forum. As Moiseh says - the Mexican trucks can only deliver goods to specific customers in the US and only pick up stuff going directly back to Mexico. They cannot pick up and deliver US goods within the US. But if anyone has ever been near places like El Paso or an other major border crossing you have seen all the truck lots and warehouses all along the highway with just about every US trucking company represented. The Mexican trucks drive over the border to the warehouse and drop of goods and pick up goods and go back to Mexico. This is costly. Load and unload and support warehousing etc. So the idea is that Mexican trucks deliver directly to customers in the US to save the costs of unload - warehouse - load - etc. Costs that are added to the price we pay at the store. Yes, we see trucks in Mexico that do not look very safe and we see drivers behaving in ways that are not safe - but anyone who has been on the road in the US knows we have those kinds of vehicles and drivers here too. I was a driver and know that most drivers are good drivers and take care of their equipment but there are always rotten eggs in every business that give that business a bad name. Same with countries - because one guy is a bad guy does not mean the entire country is bad. The US has the highest per-capita number of criminals in prison in the world - but that does not make all people in the US criminals. Same goes for Mexico. One truck does not speak for all trucks.