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 Avenue West 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 Avenue N. Mercer Street opened to two-way traffic between I-5 and 9th Ave. N in August 2012. Since then, construction has continued on nearby Fairview Avenue N and Valley Street. The first phase will be completed in the summer of 2013.
The next phase of construction, between Dexter Avenue N and 5th Avenue W, is scheduled to begin 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 and Elliott Avenue 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.
Its circuitous one-way routing slowed traffic and has often led to congestion backing up onto I-5, as well as created conditions that contributed to over 200 accidents that have occurred here every year. Its vehicle-based design has been difficult for pedestrians and bicyclists to navigate. Finally, the public infrastructure there was obsolete and in poor condition, with pavement, sidewalks, and signals that needed replacement and some utilities along the corridor being over 100 years old.
While construction on Mercer East won’t be finished until mid-2013, Mercer Street opened to two-way traffic from Dexter Avenue N to I-5 on August 27.
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 Avenue N.
The Mercer West Project will complete the two-way Mercer Street connection between I-5 and Elliott Avenue W and connect neighborhoods to the SR 99 Tunnel by moving construction west of Dexter Avenue N. The project, which will begin construction in early 2013, will widen Mercer Street between Dexter Avenue North and Fifth Avenue North for two-way traffic and modify signals and channelization to convert Mercer and Roy to two-way streets west of Fifth Avenue North. Wider sidewalks at the SR 99 Underpass and a continuous bikeway from Dexter Avenue North to Queen Anne Avenue North are also part of Phase 2.
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 in the 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