The U.S. Department of Transportation (DOT) established on Thursday tough safety requirements for Mexican motor carriers operating to and from the U.S., and required that all motor carrier safety inspectors, auditors and investigators be certified. The regulatory action, a provision of the North American Free Trade Agreement (NAFTA), will require Mexican carriers applying to operate anywhere in the U.S. to have a distinctive USDOT number. Mexican carriers will also be required to have their vehicles pass a safety inspection, undergo intensified safety monitoring during an 18-month provisional period and provide supplemental safety certifications as part of the application process. Mexican commercial vehicles will be permitted to enter the U.S. only at commercial border crossings and only when a certified motor carrier safety inspector is on duty. Regulations also include compliance with a drug and alcohol testing program and U.S. federal hours-of-service requirements. Thursday's rulemakings are among the actions that the DOT is taking to prepare for opening the border to Mexican bus and truck operations, which is expected by mid-year.