July 27, 1999 by Gerry Everding
Memorial Day. July 4th. Labor Day. There's a dark side to these icons of the American summer vacation season -- the inevitable news reports updating highway accident death tolls during the long holiday weekends. Although heavy travel volumes certainly play a role in the high accident rates associated with busy three-day summer holidays, most experts agree that another factor is likely at play -- increased driver fatigue attributed to long driving hours, lack of sleep and the demands of holiday activities.
A long, refreshing rest may be the only real solution to the dangers of driving while groggy, but, human nature being what it is, most drivers will occasionally push the boundaries of endurance and risk behind the wheel. It's a problem expected to grow worse as America's bustling 24-hour work-hard, play-hard culture adds to the national sleep deficit.
And while science has yet to find a fail-safe solution for "asleep at the wheel" driving, new research from Washington University in St. Louis and other laboratories is providing important clues on the bio-mechanics of driver fatigue and paving the way for development of on-board alarm systems capable of rousing a driver who is dozing toward catastrophe.
What is now known for certain is that driver fatigue already poses one of the leading threats to safety on the nation's roads.
According to estimates from the National Highway Traffic Safety Administration, at least 100,000 vehicle crashes, 1,500 fatalities and 71,000 injuries each year can be directly attributed to driver fatigue. In addition to human suffering, these crashes are estimated to rack up an additional $12.5 billion in costs related to diminished productivity and property loss. Others consider these estimates to be conservative, asserting that driver fatigue also plays a significant role in the nearly one million annual crashes that are generally attributed to driver inattention.
"It's fairly obvious that people shouldn't be driving when their eyes are closed, but our research suggests that fatigued drivers become increasingly susceptible to accidents long before they actually fall asleep at the wheel," said John Stern, Ph.D., professor of psychology in Arts and Sciences at Washington University and one of the world's leading authorities on eye blinks and driver fatigue.
Stern teamed up recently with researchers from several national labs for a study of how well professional truck drivers perform in a driving simulator that mimics conditions faced by long-haul big-rig operators on the nation's winding two-lane roads.
Funded by the Federal Highway Administration and the Trucking Research Institute of the American Trucking Associations, the study used sophisticated cameras, electroencephalograms and other devices to precisely measure eye and head movements, pupil diameter, and blink rates while simultaneously recording details of driver and vehicle performance.
Nine truck drivers took part in the study, which was conducted on a truck driving simulator at the Liberty Mutual Research Center for Safety and Health in Hopkinton, Mass. Two independent research groups, Applied Sciences Laboratory and the Institute for Circadian Physiology, provided and ran the sensitive equipment used to record eye movements and other bodily functions during the simulations. Stern analyzed eye data gleaned from the study.
"A majority of the off-road accidents observed during the driving simulations were preceded by eye closures of one-half second to as long as two to three seconds," Stern said, noting that a normal human blink lasts only two- or three-tenths of a second. "Lid closures that last as long as one or two seconds provide an obvious warning sign that a driver is becoming dangerously fatigued, but by this stage it may already be too late to safely alert the driver and avoid an accident."
Stern provided an overview of this research and the science behind it in his opening presentation at a recent industry technical conference on "Ocular Based Measures of Driver Alertness." He is scheduled to present additional findings from his study at "Vision and Vehicles 8," an academic and industry conference on driver fatigue to be held in Boston in late August 1999.
For more than a decade, Stern and other researchers have explored physiological characteristics associated with fatigue and the onset of sleep in the hope that a "gadget" could be devised to recognize the telltale signs of driver fatigue and issue a life-saving warning. Much of this research has focused on the trucking industry because commercial operators have more incentive to invest in and use the warning devices. Stern estimates that the devices will initially cost several thousand dollars per vehicle, but he expects the cost to drop as the gadgets become more readily available for use in passenger vehicles. The search for an effective and cost-efficient gadget appears to be heating up as several laboratories race to bring prototype devices to the marketplace.
Before the danger zone
What measures of the fatigue are these devices most likely to monitor? Stern and other researchers contend that long blinks and eye closures occur too late in the behavioral chain to be useful as predictors of impaired performance because a driver with closed eyes may already be in the danger zone.
"Alerting systems that detect late stage sleep onset will be of marginal use because danger arises much sooner as alertness fades and driver ability diminishes," Stern said. "To be of much use, alert systems must detect early signs of fatigue, since the onset of sleep is too late to take corrective action."
Stern and other researchers are now attempting to pinpoint various irregularities in eye movements that signal oncoming mental lapses -- sudden and unexpected short interruptions in mental performance that usually occur much earlier in the transition to sleep. If these mental lapses can be identified and predicted, they may prove much more useful in providing a timely "advance warning" to a driver edging toward drowsiness.
"Our research suggests that we can make predictions about various aspects of driver performance based on what we glean from the movements of a driver's eyes and that a system can eventually be developed to capture this data and use it to alert people when their driving has become significantly impaired by fatigue," Stern said. "Some researchers suggest that such a system will be available in one or two years, but I think its more likely to be five or so years down the road before a workable and affordable system is available for public use."
Stern's analysis of data from the Liberty Mutual truck driving simulator is intended to establish some baselines for how well the average truck driver performs under normal long-haul driving conditions. Future studies may weigh the fatigue-fighting effects of caffeine, conversation, music and other stimulants, but these influences were purposely eliminated from this initial study. Participants were thoroughly trained on the simulator and a benchmark measurement of well-rested performance was taken during an initial two-hour morning drive. The drivers returned at 10 p.m. and were asked to drive the simulator for four two-hour periods with a half-hour rest period between each driving session.
Throughout the driving sessions, the drivers were monitored on their ability to identify various road hazards and to execute responses as directed. For instance, drivers were given three seconds to sound the horn when a pedestrian figure appeared. The drivers' ability to quickly process information from side-view mirrors was tested by presenting a picture of an automobile grillwork in the mirror and instructing the driver to turn on the appropriate turn signal if a rectangle was missing from the grillwork.
Throughout the study, drivers' mirror gazes were generally quite brief, ranging between 0.5 and 1.5 seconds. When drivers made repeated mirror gazes, they tended to separate each gaze with a brief glance back to the driving scenario of approximately a half second.
"This suggests that drivers generally do not take their eyes off the roadway in front of them for more than 1.5 to 2 seconds, at least in this simulated scenario, in which they are driving on a two-lane road with the possibility of oncoming traffic," Stern said.
During this study, monitoring equipment also captured a range of data on actual eye closures, including one closure that lasted about four seconds. Slow rolling eye movements preceded the closure by about a half second. Within 20 seconds of the closure, the driver had an off-road accident. The accident was preceded by a flurry of eye activity, as well as head movement.
"The eyes do not have to be away from the roadway for long to invite an accident, especially on a two-lane highway," Stern said. "Obviously, on a razor-straight four-lane divided highway, a driver may be able to doze off for longer periods and still regain control of the vehicle without mishap."
A call for change
While Stern's research is shedding light on the basic science behind driver fatigue, the issue of fatigue-impaired drivers appears headed for the front burner in terms of national regulatory politics and policy. In recent years, the trucking industry has faced increasing pressure from government agencies, insurance lobbies and public interest groups to reduce fatigue-related truck accidents.
In June 1999, the National Transportation Safety Board (NTSB) issued a report criticizing the U.S. Department of Transportation for failing to develop new safety regulations to combat the growing problem of highway accidents related to driver fatigue, especially their inability over the last 10 years to make any significant revisions in rules governing how long the drivers of heavy trucks may remain behind the wheel.
High on NTSB's current list of "Most Wanted Safety Improvements" is a call for changes in federal "hours of service" regulations, which specify the length of on-duty and off-duty time for truck drivers and other transportation operators. Current rules generally prohibit commercial drivers from driving more than 10 hours or working more than 15 hours at a stretch before taking an eight-hour rest.
The NTSB has recommended changes in these rules for more than a decade, but its 1999 study found "there has been little or no action with respect to the critical need for revising hours-of-service regulations." The report also emphasized that none of the current regulations take into account modern research on human sleep and rest requirements. The NTSB has since issued new recommendations asking that the Department of Transportation take steps to establish revised "scientifically based" hours-of-service regulations within two years.
The NTSB recommendations are likely to touch off a flurry of research on driver fatigue, including efforts to evaluate the effectiveness of fatigue warning devices and to weigh the pros and cons of existing "hours-of-service" regulations. Stern contends that the answer to these and other issues may well lie in the eyes of fatigued drivers.
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