By Mark Rosekind, Ph.D.
Fatigue has been on the NTSB Most Wanted List of Transportation Safety Improvements since the List was first created in 1990. The NTSB has identified fatigue as the probable cause or a contributing factor of accidents in every mode of transportation. Based on its accident investigations, the NTSB has made more than 190 fatigue-related safety recommendations. One recent accident illustrates how fatigue can lead to tragedy.
On June 26, 2009, in Miami, Oklahoma, a commercial truck driver going 69 mph with his cruise control on ran into a line of vehicles that had stopped due to another accident. Before the truck finally stopped, it hit 6 vehicles, took 10 lives, and injured 5 more.
The Board found the Probable Cause of the accident to be:
“the driver’s fatigue, caused by the combined effects of acute sleep loss, circadian disruption associated with his shift work schedule, and mild sleep apnea, which resulted in the driver’s failure to react to slowing and stopped traffic ahead by applying the brakes or performing any evasive maneuver to avoid colliding with the traffic queue.”
The driver had not violated Federal Hours of Service (HOS) regulations and the accident showed that, while necessary, HOS regulations are not sufficient to eliminate or fully manage fatigue risks in commercial trucking.
Though this is only one example of a fatigue-related accident, it raises the question about what factors are examined to determine whether fatigue played a causal or contributory role in an accident.
Since the discovery of REM (rapid-eye-movement) sleep in the 1950s, there has been a tremendous increase in the scientific knowledge on sleep, circadian rhythms (the body clock), alertness, and performance. Generally, when examining fatigue in an accident, investigators consider the physiological factors known to impair alertness and performance. The four basic fatigue factors are:
- sleep (acute sleep loss and cumulative sleep debt),
- hours of continuous wakefulness,
- circadian factors (time of day, work/rest pattern), and
- sleep disorders.
By investigating each of these fatigue factors in detail for a minimum of 72 hours prior to an accident, it is possible to create a portrait of whether, and to what extent, fatigue played a role at the time of the accident.
Fatigue remains on the NTSB Most Wanted List and many changes are needed before this important safety issue is effectively addressed.
Mark Rosekind, Ph.D., is a Member of the National Transportation Safety Board. He is a frequent contributor to the NTSB blog.