The study to examine driver behaviour in permitted left turns has identified what researchers call an "alarming" level of risk to pedestrians crossing the street - about 4-9 per cent of the time, drivers don't even bother to look and see if there are people in the way.
As 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 mix of signals, and drivers may have to pick their way through narrow windows of oncoming traffic.
The danger is much higher than had been realised, experts warn.
"There are far more pedestrian crashes in marked crosswalks than anywhere else on roads, and pedestrians already have a false sense of security," said David Hurwitz, an assistant professor of transportation engineering at Oregon State University.
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"This study found that one key concern is permitted left turns," Hurwitz said in a statement.
As they wait to turn left, sometimes taking a narrow opportunity to lunge into a stream of oncoming traffic, drivers focus most of their attention on the vehicular traffic and the traffic signal, rather than any pedestrians crossing the street, the research showed. The heavier the traffic, the less attention paid to pedestrians.
This suggests a major level of risk to pedestrians, researchers said, if they assume that drivers not only will look for them, but will allow them to cross the street.
The problem is aggravated by "permitted" left turn signals that vary widely, from state to state and sometimes even from one city to the next.
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.