An Hours of Service extension is an allowance made by the FMCSA for a driver to drive longer than the mandated maximum driving time.
The purpose of the hours-of-service extension
The purpose of the extension is to provide drivers with an additional two hours of time to complete their run if they encounter previously unknown adverse driving conditions.
Drivers are given the ability to extend their maximum DOT driving hours by up to two hours under adverse driving conditions. Drivers are allowed to drive 13 hours (instead of 11 hours) if the adverse driving conditions couldn’t have been known or forecasted before driving began.
There are two variations of the allowed extensions: one for property-carrying drivers and one for passenger-carrying drivers.
Adverse driving conditions extension for property-carrying drivers
Drivers are allowed to extend the 11-hour maximum driving limit and 14-hour driving window by up to two hours when adverse driving conditions are encountered.
Adverse driving conditions extension for passenger-carrying drivers
Drivers are allowed to extend the 10-hour maximum driving time and 15-hour on-duty limit by up to two hours when encountering adverse driving conditions.