January 10, 2000
An artist's rendering of the proposed roundabout on SR-203 and NE 124th south of Duvall.
Courtesy of DOT.
DUVALL--Installation of a traffic control device designed to make the intersection of SR-203 and NE 124th a lot safer has been delayed by the passage of I-695, state Department of Transportation (DOT) engineers told Duvall Chamber of Commerce members last week.
The design, called a "roundabout," is commonly used in Europe and Australia, but is still relatively rare in the U.S. Engineers originally hoped to have the roundabout installed by next year, but after losing $1 billion out of the transportation budget, the state must wait on legislative approval before moving ahead with the purchase of the required rights-of-way.
The roundabout design would reduce congestion and is expected to decrease the total number of accidents there by a least one-half, engineers told Chamber members. Serious and fatal accidents are expected to decrease by one-third because the design causes drivers to slow down as they enter, engineers said.
DOT engineer Dave Edwards said the intersection of SR-203 and NE 124th is a "high-accident location" within a high-accident corridor and was first on the 1996 priority for signalization and additional channelization. Eventually, plans for signalizing the intersection were dropped due to delay and congestion factors, Edwards explained.
"Continuity on SR-203 would be disrupted by a signal, plus the accident numbers would probably remain high, due to the fact that people tend to run yellow lights," he said. "And the environmental effects would be about the same as for all the other alternatives."
Traffic signals, with their timing and maintenance, are also more costly to keep up, he said. The roundabout would cost $1.5 million to install. The state classifies SR-203 as a "rural minor arterial," with the speed limit set at 55mph, slowing to 45mph at NE 124th.
"The highway currently carries 13,000 cars a day, and those numbers are growing," Edwards said. "About 1,400 cars travel through during the peak traffic periods."
Accidents do tend to increase with a brand-new traffic feature such as this, he said, but "when people get accustomed to the new design, the number of accidents drops off significantly." He noted that many people are acquainted with traffic circles, which are larger than roundabouts.
Roundabouts originated in Europe and became popular because they have a high capacity and keep traffic flowing. Edwards said entry vehicles must yield to circulating traffic.
"By using a special geometry, the roundabout uses wide splitter islands, that with signage and illumination, direct vehicles to the right," he said.
With the roundabout, there are only eight vehicle conflict points during entering and merging, as compared to 32 for a standard intersection, which reduces the number and severity of accidents.
"It has a traffic calming effect," he said. He said the design offers ample width for buses and the many trucks that use SR-203.
"This roundabout has been designed to have the least impact on the surrounding area," he said. "Extra vegetation is included to make drivers more cautious."
The roundabout design, with its extensive landscaping, could also be used as a "gateway or community entrance" to Duvall or Carnation, Edwards said, suggesting that maintenance of the area could be taken up by local groups. But those who feel the need to "adopt" the roundabout shouldn't be in a hurry to get out their lawnmower and fertilizer.
"The design is supposed to be completed by spring, with construction planned to begin a year later," Edwards said. "But we have to wait until we get funding from the legislature to purchase the required rights-of-way and then it takes another year to complete it."
Other locations in Western Washington where roundabouts have been installed are on West Lake Sammamish Parkway, in Port Orchard, and on University Place in Tacoma.
The state is also planning a roundabout at the junction of highways 202 and 203 at Fall City, but the same funding problems will delay that as well. The Riverview School District will be studying roundabouts used in Maryland to make a determination on how it would work for the school buses, said Carol Otness, Riverview Transportation Director.
The DOT engineers will be giving the same presentation to the Carnation Chamber of Commerce at its meeting on Thursday, January 13, 8 a.m. at the Carnation Fire Hall.