Mercer Corridor: Project Background
For more than 40 years, the Mercer Corridor has been one of the City’s most significant transportation challenges. Some 80,000 vehicles at the I-5 interchange, along with growing numbers of pedestrians and bicyclists, travel the Mercer Corridor between Elliott Ave. W and I-5 each day, making it a critical east/west route for keeping people, goods, and services moving.
In early 2010, SDOT began the first phase of construction between I-5 and Dexter Ave. N and Mercer St. opened to two-way traffic between I-5 and 9th Ave. N in August 2012. Since then, construction has continued on nearby Fairview Ave. N and Valley St. The first phase will be completed in fall, 2013.
The next phase of construction, between Dexter Ave. N and 5th Ave. W, began in early spring 2013 and is anticipated to be complete by mid-2015. When complete, the Mercer Corridor will carry two-way traffic between I-5 5th Ave. W and connect Seattle neighborhoods to the north portal of the SR 99 Tunnel.
A two-way Mercer Corridor improves mobility for all modes of transportation:
The “Mercer Mess” has been a major bottleneck in the Seattle for decades, and has been hindering access to Seattle’s fastest growing neighborhood, South Lake Union. The old Mercer and Valley streets couplet was constructed in the late 1950s as a temporary solution intended to provide access to I-5 as it was being built.
The previous configuration of Mercer and Valley streets is shown below.
Its circuitous one-way routing slowed traffic, often led to congestion backing up onto I-5 and created conditions that contributed to over 200 accidents that occurred nearby each year. The vehicle-based design was difficult for pedestrians and bicyclists to navigate and the public infrastructure was obsolete and in poor condition. The pavement, sidewalks, and signals need replacement as some utilities along the corridor are over 100 years old.
While construction on Mercer East won’t be finished until fall 2013, Mercer St. opened to two-way traffic from Dexter Ave. N to I-5 on August 27, 2012.
There are now three eastbound lanes traveling onto I-5 (the same number of through lanes to I-5 that Mercer previously had), three westbound lanes (currently operating from I-5 to 9th Avenue N), plus a far right through lane for vehicles traveling to Capitol Hill (as previously existed), and a new left-turn lane onto Fairview Ave. N.
The Mercer West Project will complete the two-way Mercer Street connection between I-5 and 5th Ave. W and connect neighborhoods to the SR 99 Tunnel by moving construction west of Dexter Ave. N. The project, which began construction in early 2013, will widen Mercer St. between Dexter Ave. N and 5th Ave. N for two-way traffic and modify signals and channelization to convert Mercer and Roy to two-way streets west of 5th Ave. N. Wider sidewalks at the SR 99 Underpass and a continuous bikeway from Dexter Ave. N to Queen Anne Ave. N are also part of the West Phase.
Widened Mercer Underpass
The widened Mercer Underpass will provide three lanes of traffic in each direction, left turn lanes, wider sidewalks (considerably wider than the current 5’ sidewalk width) and a bike path.
Additional project benefits ofthe underpass area include:
Tree Additions and Removals
Mercer West will plant 2 new trees for every tree removed during the project.
Converting Mercer and Roy streets to two-way operation