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Status Report, Vol. 50, No. 2 | March 3, 2015 Subscribe

Intersections challenge older drivers

Safely navigating intersections continues to vex older drivers, who look but don't always see conflicts with other vehicles, new IIHS research finds.

Numerous studies have shown that older drivers are overinvolved in angle, overtaking, merging and intersection crashes, especially those involving left turns (see Status Report special issue: older drivers, March 19, 2007).

In the second of a pair of new studies on older drivers, IIHS researchers used information from a national in-depth study of passenger vehicle crashes to examine critical driver factors that led to crashes among drivers 70 and older, compared with those of drivers ages 35-54. Data are from the National Highway Traffic Safety Administration's National Motor Vehicle Crash Causation Survey (NMVCCS), a nationally representative sample of 5,470 police-reported passenger vehicle crashes during 2005-07 for which emergency medical services were dispatched.

Crash investigators coded a driver factor as the critical reason in nearly all crashes involving drivers ages 35-54 and 70 and older. The NMVCCS database defines the critical reason as the cause of the critical pre-crash event, defined as the event that made the crash inevitable.

Errors that older drivers frequently make differ in important ways from those of middle-age drivers. The most common critical error among older drivers was inadequate surveillance (33 percent), followed by misjudging the length of a gap between vehicles or another vehicle's speed, failure to obey traffic controls or other illegal maneuvers, medical events, and daydreaming (6 percent each). Inadequate surveillance and gap or speed misjudgment errors were significantly more prevalent among older drivers than middle-age drivers.

Surveillance errors included looking but not seeing and failing to look. Drivers 70 and older had the most trouble with the former. Among older drivers who made critical surveillance errors, 71 percent of their crashes were attributed to looking but not seeing another vehicle or failing to see a traffic control as opposed to failing to look, compared with 40 percent of middle-age drivers. Middle-age drivers were more likely to fail to look at all.

About two-thirds of older drivers' inadequate surveillance errors and 77 percent of their gap or speed misjudgment errors were made when they turned left at intersections.

Compared with middle-age drivers, physical factors were most often the cause when older drivers left their lanes or traveled off the road prior to crashing, which occurred in about a quarter of crashes. Most of these physical-factor events involved blackouts, drowsiness or seizures. In contrast, when middle-age drivers were involved in these types of crashes it was more often due to distraction, speeding or overcompensating when drifting than a physical or medical factor.

Older drivers overall were less likely than middle-age drivers to have made overcompensation errors or to have driven too fast for conditions, a curve or to respond to others' actions.

"Errors older drivers commonly make stem from the typical issues associated with aging. These include declines in cognitive, perceptual and physical abilities," explains Anne McCartt, a co-author of the study and the Institute's senior vice president for research.

Top driver factors in crashes, by driver age

ages 70+ ages 35-54
Inadequate surveillance 33% 22%
Gap/speed misjudgement 6% 3%
Medical events 6% 4%
Failure to obey traffic controls or other illegal maneuvers 6% 4%
Daydreaming 6% 4%

For example, the study suggests that visual impairments can affect a driver's ability to judge gaps between vehicles or how fast other vehicles are traveling. Older drivers who made this critical error were 7 times as likely to have a diagnosed visual impairment as older drivers who made other critical errors.

Countermeasures that simplify or remove the need to make left turns across traffic, such as roundabouts, protected left-turn signals and diverging diamond intersection designs could decrease the frequency of inadequate surveillance and gap or speed misjudgment errors. In the future, vehicle-to-vehicle and vehicle-to-infrastructure communications also may help protect older drivers from these errors.

Replacing a traffic signal or stop sign with a roundabout improves safety because the roundabout's tight circle forces drivers to slow down, and traffic flows in the same direction (see "When roadway design options are wide open, why not build a roundabout?" Nov. 19, 2005). The most dangerous types of intersection crashes — right-angle, left-turn and head-on collisions — are essentially eliminated with roundabouts. Where roundabouts have been installed, crashes have declined about 40 percent, and those involving injuries have been reduced about 80 percent (see "Roundabouts sharply reduce crashes, study finds," May 13, 2000).

Despite the safety benefits, older drivers remain wary of roundabouts. Older drivers are less likely than younger drivers to favor roundabouts and may go out of their way to avoid them, IIHS research has shown (see "Two-lane roundabouts bring benefits but also some confusion," March 14, 2013).

MAIN STORY
Why older drivers are dying less often

The fatality rate among drivers age 75 and older has improved because they are involved in fewer crashes per mile traveled and are surviving side impacts more often.

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