Plenty can be done to unclog traffic on Interstate 5, but it’s almost all costly in one way or another. Adding lanes, especially through downtown Seattle, is enormously expensive. Adding tolls would reduce traffic, carries its own obvious costs.
Even if the city and state wanted to do so, there’s no easy way to widen Interstate 5 through Seattle. The highway’s west side is lined with buildings and businesses, some less than 100 feet from mainline traffic.
The east side of the highway is the same, but even more daunting. A half-century ago, when the highway was being built, the uphill neighborhoods, Capitol Hill and First Hill, became unstable, with small landslides threatening to devolve into larger, catastrophic ones.
Whole blocks of buildings could have slid into the new I-5 canyon below.
The solution: retaining walls on I-5’s east side have steel and cement columns drilled 120 feet deep to hold up the hillside. Those columns are not easily moved.
“If you’re looking to add capacity to I-5 — it is so expensive and so hard to widen that road — you could do it, no question engineers could do it, but what are you willing to pay for it?” said Mark Hallenbeck, director of the Washington State Transportation Center. “Are you ready to pay four bucks, six bucks every time you drive it? The answer, suddenly, is no.”
A 2007 WSDOT study outlined dozens of other ideas that could improve traffic flow on I-5 around Seattle.
WSDOT could, at little cost, transform I-5’s northbound shoulder between Olive Way and 520 into a transit-only lane. That would reduce evening commute times by an estimated two minutes for the two dozen bus routes that travel that stretch of I-5.
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