What is the HOS adverse driving conditions exemption?

The adverse driving conditions exemption is a provision made by the FMCSA as part of their hours-of-service regulations. 

The adverse driving conditions exemptions says that drivers are allowed to extend their allotted driving time per day if they’re experiencing adverse driving conditions. Per the exemption, property-carrying drivers may extend their 11-hour driving limit and 14-hour driving window by two hours, and passenger-carrying drivers may extend their 10-hour driving time and 15-hour on-duty limit by up to two hours when encountering adverse conditions.