David Hurwitz of Oregon State University said opposed to a "protected" left turn, in which a solid green arrow gives a driver the complete right of way in a left-turn lane, a "permitted" left turn is often allowed by a confusing hodgepodge of signals.
Permitted left turn signals vary widely from state to state and sometimes even from city to city, Hurwitz said. Such turns might be allowed by a circular green light, a flashing circular yellow light, a flashing circular red light, or even a flashing yellow arrow.
Hurwitz used a sophisticated driving simulator, which allows test subjects to see, experience and react to realistic driving experiences while scientists study their reactions and behavior. This study involved subjects experiencing 620 permitted left turn maneuvers.
"This study found that one key concern is permitted left turns," Hurwitz said in a statement.
The study found as drivers waited to turn left, they focused most of their attention on the vehicular traffic and the traffic signal, rather than any pedestrians crossing the street. The heavier the traffic, the less attention paid to pedestrians.
In a controlled analysis in a full-scale driving simulator that monitored specific eye movements, the engineers found that 5 percent to 10 percent of the time the driver didn't even look to see if a pedestrian was there before moving into the intersection.
The findings are scheduled to be presented at this year's Driving Assessment Conference in New York.