For Mexico the road trains exist in a very small form due to the highway sizes and streets in the principal cities, and there are only permitted 2 trailers joined with a pup or dolly created for this purpose, recently the regulations tend to be more severe and strict to avoid overloading and frequent accident chance, to adhere to the federal rules of transportation. Truck drivers must obtain a certificate to certify that the driver is capable to manipulate and drive that type of vehicle.