The primary safety uses of highway mile markers is to help locate motorists in need of aid and alert drivers of any hazardous roadway conditions. When a motorist calls for emergency or roadside assistance, knowing what mile marker is nearby helps to get a faster response. Motorist emergency call boxes and highway exit signs also serve as mile markers on many highways. Mile markers also are helpful to know where road crews are working on highways.
Mile markers change as drivers cross state lines. In some places, they change as motorists cross county lines. Miles are numbered either south to north or west to east. When motorists report which mile marker they're closest to, it's important to also note the direction of travel.
When the Department of Transportation issues a traffic warning, such as road construction, lane closures, flooding or an accident, stating which mile markers or exits are nearby helps motorists to prepare for any resulting changes in traffic patterns or roadway congestion. If motorists know where issues are ahead of time, they can pull into another traffic lane, slow down, pull off the highway to replenish gas, find an alternate route or generally be more aware of driving conditions before approaching a potential safety hazard.