August 3, 2010
Putting Speed at the Top of the Agenda
The City of Portland is likely to put getting local control over speed limits at the top of its Legislative Agenda for the next session. BikePortland.org has excellent coverage.
I couldn't agree more. The idea that speeds on local streets should be controlled by a committee in Salem that doesn't even meet any more is simply outdated and doesn't allow a proper focus on safety.
August 3, 2010 10:57 AM
This is interesting. The idea that a highway agency whose almost sole focus is moving cars faster should be setting speed limits on community streets, falls somewhere between unethical and malicious.
Speed limits of 35 on streets like Burnside, 50th, and others, it's no wonder so many are injured and killed on our streets.
I am disappointed that PBOT would only pursue this for bike streets, as it's a larger safety issue. Why would ODOT object? Do they like people being injured and killed? I think not. Do they not understand the connection between speed and injury severity? Why do they feel the need to micromanage cities, especially Portland, whose expertise is far more sophisticated than ODOT?
August 3, 2010 2:32 PM
Unit Wrote: "Why do they feel the need to micromanage cities, especially Portland, whose expertise is far more sophisticated than ODOT?"
That is exactly what ODOT has intended. Cities often lack the engineering experience to assign speed limits. With the decisions at a local level they are more far susceptible to political influence; for safer-feeling (not actually safer) or even revenue generation. Portland and a few other large cities in Oregon might be the exception, not the rule. Even the, PBOT is certainly is not immune to political influences.
People tend to drive at a comfortable speed which may or may not correlate with the posted speed limit. Build a two lane neighborhood street with a 48-foot profile and people will drive 40 mph even if it is posted 25 mph. Design is much more important than the signs.
August 3, 2010 6:31 PM
Michael, Portland Afoot Says:
What's the social science say on speed limits? Last time I discussed this with a traffic engineer, they claimed the tests show that speed limits have zero affect on drivers' behavior.
That just doesn't ring true for me -- and in retrospect, the evidence the engineer as proof demonstrated only that speed limits have zero affect on whether the driver drives above or below the posted speed ... but not on whether the driver drives 10 mph too fast rather than 20 mph too fast.
Anyway, I'm skeptical of the notion that speed limits, especially without accompanying enforcement dollars, actually improve safety.
August 3, 2010 6:32 PM
Michael, Portland Afoot Says:
Wrong "effect"! Red writer's face.
August 3, 2010 6:39 PM
Bob R. Says:
Does that make you "disaffected"? :-)
In my experience, on I-5 in the California central valley, as speed limits were increased in the last decade, average speeds and top speeds picked up considerably. People often went 10mi+ over the speed limit, regardless of what the speed limit was.
(And can someone explain to me: If, back when the top speed limit was 65 in California, mountainous sections of road were considered less "safe" and were marked as 55mph, why did the mountainous sections get increased when the flat sections got increased in later year? Are they suddenly more "safe"?)
August 3, 2010 7:34 PM
There's a reason that posted speeds are often 10MPH or more below design speeds...
August 4, 2010 6:30 AM
Just Saying Says:
"Design is much more important than the signs."
I think this is correct. But you aren't going to get a street engineered for 15 mph if the posted speed is 25.
There are also rules on when and where traffic calming can be used to reduce speeds. They are set based on how many people are exceeding the posted speed. So if most people are going under 25 mph on a local street, you can't put in traffic calming. But 25 mph is not safe for pedestrians, kids, dogs etc.
And, frankly, politics ought to determine speeds. The balance between safety and efficiency is not an engineering question.
August 4, 2010 3:52 PM
The contention that a State highway agency has a better idea of what's an appopriate speed for a neighborhood street than the local jurisdiction is preposterous. Some Salem bureaucrat knows what's best for downtown Portland? You don't need an engineer - you just need a little common sense.
A little background is in order: ODOT uses the 85th %-ile speed to set speed limits. This is a mostly arbitrary national standard that was set based on studies of rural highways. Putting aside the fact that it was an arbitrary point to set the standard, the application of a rural-based policy to an urban environment is inappropriate.
Any rational decision would include consideration of the safety of pedestrians, bicyclsts, schoolchildren, the elderly, and probably some consideration to the goals of the affected community. Of course, ODOT's model looks primarily at the speeds drivers want to drive; safety is secondary. When someone gets run over and killed or maimed (a frequent occurence in Oregon), tough cookies. And yes, speed is often a factor.
Speed limits on their own have some small effect on speed, although artifically low limits do encourage speeding. By the same token, engineers can't design a 25 mph street if the posted limit is 35 mph. The classic chicken-and-egg problem.
And frankly, PBOT's safety record blows away ODOT's; PBOT has been making their streets safer for years, ODOT not so much. Which do you think cares more about your safety as a city resident?
This is why you don't want a rural highway agency setting neighborhood street standards - an absolutely bizarre and arcane element of our state bureaucracy.