HOS stands for Hours of Service — the FMCSA rules that cap how many hours a commercial driver can be behind the wheel and on duty within a given window, and mandate rest breaks. The goal is to keep tired drivers off the road.
These limits shape everything a dispatcher plans, because a driver can only legally cover so many miles per day. Compliance is tracked automatically by the ELD, and running out of hours mid-trip can force a layover until the driver is legal to drive again.