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For a show about red lights, it's interesting how much time we spent today in the yellow!
Lisa and other folks wanted more details from Greg Raisman about how the city times its yellow signals. So I talked to him after the show and asked if he could provide more specific information. He emailed:
In Portland, we use the nationally accepted method prescribed by the Institute of Transportation Engineers (ITE) to program yellow light timing. This approach considers actual approach speed of traffic and the grade, or slope, of the road leading to the intersection. Generally, the faster that traffic is going and the steeper a downhill grade approaching a traffic signal, the more time is given for the yellow phase.
In Portland, we have consistently provided a little extra time on top of what ITE has recommended.
Here are details for the city's camera'd intersections:
(If anyone wants to check this out with a stopwatch, feel free.)
Raisman also followed up on the disagreement that came up at the end of the show. Emily asked what one thing both he and Jim Baxter, from the National Motorists Association, would do to improve road safety. Raisman said people should driver slower, and not drink and drive. Baxter said drivers should be more attentive and less distracted.
This is what Raisman wrote in after the show:
In Oregon, approximately 40% of traffic fatalities involve speed and 40% of traffic fatalities involve impaired driving. Some of these crashes involve both speed and impairment. High speeds lead to a higher incidence of crashes because it takes longer to stop for unexpected circumstances. When crashes do occur, the higher speeds result in greater severity of the crash as thousands of pounds of metal are crushed against each other. Impairment is a major contributor because drivers are less able to negotiate on the road and because it effects their ability to respond to the presence of other travelers.
I called Baxter up to talk about all of this. Interestingly, he didn't argue with the idea that 40% of Oregon's fatal crashes would involve speed because, as he noted, "everyone speeds." Instead, he stressed the importance of looking at the "primary causative factor." He said that, nationally, speeding is the primary cause of crashes only 2-4% of the time, and alcohol only 5-6% of the time. I've asked him to send studies along and will post them when he does.
One final note: Dogbeard signed on after the show to ask if the new video cameras start recording before a violation has been detected. It turns out that they're recording all the time — like security cameras in a convenience store — in a 30-day loop, but officers only watch the eight-second clips after an infraction has been detected.
Have a great Labor Day Weekend!
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