Driver fatigue is a major contributor to road crashes. Fatigue decreases our ability to operate vehicles safely and reduces our "situational alertness."
One recent study found a tell-tale sign that you may be too tired to drive.
"There was basically more relaxation in the muscles of the neck and the back, signaling this enhanced, what we call, parasympathetic tone kicking in, relaxation," Dr. Reena Mehra said.
Dr. Mehra also says if you find yourself struggling to focus or blinking a lot, you're too tired to drive. Other signs include rubbing your eyes and daydreaming.
If you're already behind the wheel and begin to drift while driving, you're yawning, or you can't remember the last few miles, you're fatigued and should stop immediately.
Dr. Mehra said other signs you're too tired to drive include rolling down the window to get some air on your face or turning up the volume on the radio to stay awake. Both are no no's.
A recent Virginia Tech Transportation Institute study found driver fatigue causes as many as 20 percent of all car crashes and that people ages 18-20 years old account for more fatigue-related crashes than any other age group.
Dr. Mehra said you must listen to what your body is trying to tell you.
"If these things could, sort of, alert someone, if you will, to the fact that they are too drowsy to be behind the wheel then perhaps we could potentially save some lives," she said.
If you are going to be driving long distances, especially at night, put together a plan or bring someone along to share the responsibility.