ARLINGTON, Va. --- Studies going back decades reveal that older drivers are over-represented in collisions at intersections. Forty percent of the fatal collisions of people 70 and older, compared with 23 percent of the crashes of 35-54 year-olds, occur at intersections and involve other vehicles. What mistakes are leading older motorists to get into intersection crashes? A new Insurance Institute for Highway Safety study focuses on intersection crashes involving more than 200 drivers in three age groups -- two groups of older drivers (70-79 years old and 80- plus) and a comparison group of 35-54 year-olds. The researchers studied crashes involving injuries on Connecticut roads during 2003-04, examining police reports and photographs of the intersections where the crashes occurred. The researchers also interviewed the drivers found at fault in the collisions. "The interviews with the at-fault drivers are what set this study apart from earlier ones, giving a clearer picture of the mistakes people of various ages are making behind the wheel and why," said Anne McCartt, Institute senior vice president for research. "Previous studies have compared the kinds of crashes older versus younger drivers get into, and in the interviews we delved further into the underlying reasons." The types of crashes in which drivers 70-plus years old are at fault differ from crashes for which 35-54 year-olds are responsible. These differences amplify with age so that the crashes of drivers 80 and older also differ from those of 70-79 year-olds. Among the drivers in Connecticut, rear-end crashes accounted for a lower proportion of 80-plus drivers' intersection crashes. Both groups of older drivers, those 70-79 and 80-plus, had lower proportions of run-off-the-road crashes than 35-54 year-olds. In contrast, failure to yield the right of way to other vehicles led to more than half of the intersection crashes for which the oldest drivers were responsible. This compares with about one-third of the intersection crashes of 70-79 year-olds and about one-fourth of those involving 35-54 year-olds. Reasons for the intersection crashes varied by driver age. People 70-79 made more evaluation errors than drivers of other ages. That is, they saw potentially conflicting vehicles but misjudged whether there was time to proceed. Drivers in the other age groups (35-54 and 80-plus) more often failed to see potentially conflicting vehicles. The 35-54 year-olds said it was because they became distracted, while most of the drivers 80-plus said they were looking but simply didn't see the conflict. McCartt said the failure to see other vehicles "may be due to increases in vision impairments, which escalate rapidly after about age 75. Another factor could involve the complexity of urban intersections, with vehicles traveling in multiple directions. Older drivers may experience decreasing ability to process the multiple sources of information at once and maneuver safely." Range of head movement might also be a factor in older drivers' crashes. These ranges have been found to decrease with age, which could hinder a driver's ability to see potentially conflicting vehicles. Whatever the reasons for the intersection crashes, those involving failure to yield occurred more often where traffic is controlled by stop signs than at intersections with signal lights (more rear-end crashes occurred at the signals). Fifty-nine percent of the failure-to-yield crashes occurred at stop signs, and 50 percent of these crashes occurred while motorists were turning left. The proportions didn't vary much across the three age groups. Other studies also indicate an age effect. For example, a 2002 study by University of Kentucky researchers found that each advancing year of age after 65 increases by 8 percent the odds of getting into a crash that involves turning left. Not surprisingly, it's the converse in Australia. Motorists there travel on the left side of the road, and as Australian drivers get older they become over-represented in collisions involving right turns. Older people represent an increasing proportion of the U.S. population, and this trend is escalating as baby boomers age. Older people are keeping their driver's licenses longer than in past years, and they're driving more miles. For these reasons, it's becoming increasingly important to find ways to reduce the frequency and severity of older people's crashes, including the collisions that occur at intersections. One way would be to add green arrows to protect left turns at intersections controlled by signal lights. Then motorists, including older people, wouldn't have to judge how fast vehicles are approaching from the other direction and whether there's enough time to turn in front of them. Another approach would be to construct more roundabouts in place of intersections with traffic lights and stop signs. These circular intersections have design features that slow traffic and promote efficient flow. They also might be easier for older drivers to navigate because vehicles go through them in one direction, not from multiple directions.