2-way Mercer won't assure faster traffic flow, study says

A newly released traffic study predicts that if Seattle widens Mercer Street for two-way travel, a drive through the area won't necessarily be faster than it is today.

Trips westbound from Interstate 5 to Seattle Center would improve by 2-½ to 4 minutes in the morning, because drivers won't have to make a pair of turns to reach Valley Street. Eastbound trips would be about the same. But in the afternoon, most trips in both directions would be slower, the study says.

Those conclusions mostly jibe with an earlier report and with recent comments by city officials. Backers now portray a Mercer Street rebuilding not as a boon for motorists, but as a way to give the growing neighborhood a greener, calmer, safer street grid.

On Monday, the City Council voted 8-1 to release $14 million this year for engineering and right-of-way buys on the $201 million project. Council members and the Seattle Department of Transportation (SDOT) would not release the traffic study Monday. They did so Tuesday, after asking permission from federal and state project partners, an SDOT spokesman said.

Some other predictions in the study:

• Valley Street, to be narrowed from five street lanes to two, plus bike lanes, would "promote a pedestrian- and bicycle-friendly atmosphere" next to Lake Union Park.

• The junction of Mercer with Fairview Avenue North would improve, but it would still be sluggish.

• "High delays" would occur where Mercer, Broad Street and Ninth Avenue converge at the west end of the rebuilt corridor.

• On-street parking would be provided on stretches of Mercer and Valley streets. One option would reduce Mercer by one lane — and boost a 10-minute eastbound peak trip to 18 minutes. The report says there's also a benefit: separating sidewalks from busy traffic.

Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com