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Triangle solutions ring follow
Design plans for the Triangle project in the southern part of Federal Way hit a snag this month, after closer inspection revealed traffic at the intersection of State Route 161 and South 356th Street wont get any better once an off-ramp at South 352nd is built.
After dismissing a few less-feasible ideas including a proposal to build the states first-ever, three-lane roundabout city officials are now faced with building an awkward but cost-effective intersection that ultimately wont meet the citys standard for levels of service by 2030.
Still, city traffic engineer Rick Perez said the new information isnt necessarily a set-back for the project.
Initially, South 352nd appeared to have some significant advantages, but the advantages didnt outweigh the drawbacks, he said.
The Triangle project is a joint venture between the state Department of Transportation (DOT) and the cities of Milton and Federal Way to improve the high-accident corridor where three heavily-traveled highways Interstate 5 and State Routes 18 and 161 converge. Design plans include adding flyover ramps so drivers wont have to weave around each other to merge on and off the ramps.
Earlier this year, the DOT evaluated two design options that would, on paper, improve access from SR-161 to I-5. One was a northbound off-ramp to Milton Road near South 369th Street, and the other was a southbound off-ramp to South 352nd.
The DOT analysis showed the Milton Road off-ramp would only serve about 100 vehicles during the evening peak hours and wouldnt necessarily improve traffic at the rest of the interchange. It also would disrupt service at the weigh station on Pacific Highway South. DOT officials abandoned that option.
But when they looked more closely at the other option, the southbound ramp to South 352nd, they discovered it also had inherent flaws.
DOTs analysis showed more than 400 vehicles an hour would use the South 352nd ramp during the evening peak hour, which would provide a significant benefit to traffic at the intersection of SR-161 and South 356th. But the ramp would severely deviate from DOT design standards because of the grade, which was so steep it didnt pan out, Perez said.
To make it meet design standards, it would have to be stretched out into a long, sloping ramp one that would prohibit left turns into the driveways of the Home Depot and Costco stores on South 352nd. Considering the design deviations, and in anticipation of the outcry from the commercial district, DOT abandoned the South 352nd option, too.
But the removal of both options leaves a significant amount of traffic at the intersection of SR-161 and South 356th, which motivated DOT and city traffic engineers to think of options to mitigate traffic flows and still meet the citys level of service policies over the next few decades.
City engineers added some new language reflecting the need to upgrade the intersection into the citys transportation improvement plan, and officials crunched traffic numbers. But they couldnt find a way to realign the intersection to improve traffic.
The simplest solution and the one Perez said he reluctantly recommended was to realign 16th Avenue South to create a five-legged intersection controlled by traffic signals. The intersection would control traffic along the streets and also serve as the off-ramp to SR-161. Though its simple, the solution isnt expected to be cheap, and it wont meet the citys level of service requirements by the year 2030, Perez said.
Its not an insignificant expense, and because its not part of the Triangle project, the states not interested in paying for it, he said. Theres still some issues of how the city will address it. It appears to be the most prudent decision DOT could make.
Level of service how far traffic backs up at an intersection and how many lights people have to sit through ultimately wont matter because state freeways arent required to meet growth management conditions. In practice, though, well be operating the traffic signal and well be getting the complaints from commuters who have to sit through the red lights, Perez said.
In addition, to build the five-legged intersection, the city will have to widen SR-161 from South 348th Street.
But Perez claimed traffic at the intersection probably wont be much worse 25 years from now than it is today.
In the grand scheme of things, its really not that bad, but is there something we could do to make it better? he said.
Environmental analysis for the Triangle project is underway and a report is expected next August, after opportunities for public comment. Traffic engineers and city planners expect a finding of no significant environmental impact by the project in January 2007.
Since the voter failure Nov. 8 of Initiative 912, which would have repealed the states 9-cent gas tax increase, the project will receive $100 million in state funding next year. DOT is currently using $6.6 million in federal money for right-of-way acquisition, and Perez said city officials last week heard of another $3 million in federal money for the project.
Construction, which could cost between $130 million and $150 million, is expected to begin in 2009 and take between two and three years for completion.
Staff writer Erica Hall: 925-5565, firstname.lastname@example.org