Will a Canadian driver, complying with the Canadian hours of service regulations while driving in Canada, be in violation of the U.S. 10-hour rule when he enters the U.S.?
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No. Canadian drivers are required to comply with the U.S. Federal Motor Carrier Safety Regulations only when operating in the United States. Also, an American driver may comply with the Canadian hours of service regulations while driving in Canada. Upon re-entering the United States, however, the driver is subject to all of the requirements of Part 395, including the 10- and 15-hour rules, and the 60- or 70-hour rules applicable to the previous 7 or 8 consecutive days.
In other words, a driver who takes full advantage of Canadian law may have to stop driving for a time immediately after entering to the U.S. in order to restore compliance with Part 395. Despite its possible effect on decisions a U.S. driver must make while in Canada, this interpretation does not involve an exercise of extraterritorial jurisdiction.
Source: CVSA official interpretations web site