Turn on flashers and the dome light. Stay off the roadway and get passengers away from the vehicle. Of course, don't drink and drive. Almost half of all fatal crashes involve alcohol. For longer trips, allow enough travel time for frequent breaks for rest, snacks and exercise.
Drowsiness can reduce reaction time almost as much as drinking.
If you're too tired to drive, stop and get rest. Danger signs of fatigue include eye strain, blurrred vision, head dropping, yawning, swaying out of the lane or an urge to close your eyes. If you notice that a car is straddling the center lines, weaving, making wide turns, stopping abruptly or responding slowly to traffic signals, the driver may be impaired. Avoid an impaired driver by slowing down to increase following distance. If the impaired driver is behind, turn right at the nearest corner.