COLUMBIA — The flash of brake lights reflecting against icy streets has become a common occurrence in Columbia’s neighborhoods over the past few days.
But Sixth Ward Councilwoman Barbara Hoppe would like to see drivers slowing down even in the absence of the frozen hazard. The former Street Standards Committee member is pushing to reduce the city’s unposted speed limit to 25 mph and to eliminate existing 30-mph signs in an effort to make residential streets safer for pedestrians.
“Since I’ve proposed that, people I’ve talked with have encouraged me to lower it to 20 instead of 25,” she said. “I thought that was interesting.”
Hoppe said lowering residential speed limits has been a big issue for her for nearly 20 years.
“I think we’re wasting a lot of council time when the problem comes up over and over and over again,” she said. “What I’m really looking at is a policy that can help address the situation comprehensively or overall rather than street by street.”
In 2002, the City Council tried to do just that by modifying the subdivision ordinance to prohibit straightaways longer than 800 feet for streets designed primarily for access in small areas.
Long straightaways, city traffic engineer Richard Stone said, are typically avoided in road construction because “drivers sometimes gradually increase speeds without even noticing it,” he said. “So having curves, turns or roadway modifications” can provide visual cues to the driver to maintain a slower speed.
The 800-foot limit, however, applies only to subdivisions constructed after 2002, meaning neighborhoods built before then can be at high risk for speed violations.
Engineering Speed Limits
Traffic engineers typically set speed limits at what is known as the 85th percentile, the speed at which 85 percent of drivers are traveling at or below. Because this is the speed most drivers feel comfortable with, research has shown it is safest to erect a speed limit as close to that number as possible.
Speed limits that exceed the 85th percentile historically lead to higher accident rates and more resident requests for traffic calming.
For most residential streets, the 85th-percentile speed is between 33 and 37 mph, Stone said. That speed already is higher than the current limit, to say nothing of Hoppe’s proposed 25 mph.
Other criteria include accident history and adjacent speed limits. The least important criterion, according to a U.S. Department of Transportation survey of city traffic engineers, is pedestrians.
Hoppe said pedestrians should “absolutely” be a bigger factor in selecting a speed limit.
“I have talked with some key people in the PedNet group that has been working for years to make Columbia more pedestrian friendly, and they seemed very supportive of reducing the speed limit,” she said.
The city enacts “traffic calming” measures to slow down drivers on a case-by-case basis. Stone said the city is looking at two residential streets for traffic calming: Rainbow Trout Drive and Upland Creek Road. Both have straightaways longer than the modified ordinance allows and 85th-percentile speeds greater than 40 mph.
Methods of traffic calming, outlined in a report by Stone to the City Council, include installing signs, modifying roadway, and increasing enforcement.
New signs and roadway modifications, however, carry a hefty price tag. Speed humps, which the U.S. Department of Transportation has found to be the most effective way to slow traffic, can reduce average speeds by as much as 5 mph but would cost more than $1,000 each. Adding curves to existing roads would be even more expensive. Stone estimated it would cost the city $255,000 to add and replace more than 1,000 signs to accommodate a lower speed limit.
Hoppe, however, is not deterred by what she said are inflated numbers.
“Those cost estimates have a big question mark around (them),” she said, explaining that she doesn’t think new signs would be necessary. She suggested the city save money by recycling existing 30-mph signs and relying on a few signs at the city’s boundaries to declare that the new speed limit is 25 mph citywide unless otherwise posted.
Stone, however, was not optimistic that lowering an unposted speed limit alone would have a meaningful impact.
“Now it may very well be that Columbia is different than everybody else and we actually do get better compliance, but that’s not what the research shows,” Stone said, citing two U.S. Department of Transportation studies.
Hoppe expressed doubts. “I’m sure if we had 50-mph speed limits, that would affect behavior, so there’s a lot of questions in that statement,” she said, noting that people slowed down when highway speed limits were reduced to 55 mph during the oil crisis.
The third way to produce traffic calming — increased enforcement — often is unpopular but has been shown to decrease average speeds by as much as 14 percent. Hoppe doesn’t think enforcement would address the problem.
“Enforcing a 30-mph speed limit when 30 mph is way too fast doesn’t solve the problem,” she said. “We can have the same existing enforcement, but people will be getting the message that 30 is not appropriate.”
Lowering Columbia’s unposted speed limits to 25 mph would not be without precedent. Of the 31 cities selected in a 2002 survey of locales with sizes and demographic characteristics similar to Columbia, 19 had unposted limits of 25 mph. One other — Austin, Texas — had a speed limit of 25 mph on the majority of its residential streets, even though the citywide limit was 30 mph.
Hoppe said she is updating the list and conducting additional research.
“Actually,” she said, “what brought it to my attention (was) a year ago when I was traveling through Colorado Springs,” which is bigger than Columbia. “I saw a sign that said 25 mph unless otherwise posted, and I thought that was a really good idea.”
But has the Colorado Springs limit, lowered in August 2003, been effective at slowing down cars?
“Typically not, to be very honest with you,” said Dave Krauth, principal traffic engineer in Colorado Springs. What it has done, he said, is create a source of speeding-ticket revenue that has enabled the city to go through with more expensive traffic-calming techniques.
Increased enforcement, Krauth said, has “shown people that we mean business.”
Hoppe said that once she’s done her research, she hopes to put speed limits on the agenda for a council work session.