How We Decide Where to Install Traffic Signals

We have a new and improved process for deciding where to install new traffic signals.

We’re now using data on expected growth, crash history, costs for partnering with developers, and equity to prioritize the roughly 9,000 intersections throughout Seattle without signals.

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Each year the top 10 intersections by these metrics are analyzed and prioritized, with an emphasis on crash history. We also check if the intersection meets federal standards for new signals. In many cases, a new traffic signal is not the best treatment for an intersection and a less costly treatment, such as a four-way stop or turn restriction, are more appropriate–especially in situations where traffic volume isn’t high.

In the past, we’ve installed new signals primarily after public feedback, generally one or two new signals per year. But, this process was costly to administer, difficult to prioritize, did not adequately consider crash history, and ignored intersections that weren’t publicly requested.

We’ll be applying the new process to both new signal installations and left turn improvements. We hope this new process will do a better job of adding signals at intersections where they can do the most good for the most number of people.

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2017 will be a transition year between our existing prioritization process and our new process. With that said, the number of intersections to be analyzed is slightly higher than what will be analyzed in the coming years.  Below is a list of intersections to be analyzed for possible improvements:

Left Turns:
o Martin Luther King Jr Way S and S McClellan St
o 25th Ave NE and NE 75th St
o 6th Ave and James St
o Denny Way and Dexter Ave N
o 12th Ave S and S Weller St
o Boren Ave and Pike St
o 15th Ave NE and NE 50th St
o 23rd Ave E and E John St
o Martin Luther King Jr Way S and S Cloverdale St
o 2nd Ave and Denny Way

New Signals
o E Marginal Way S and S Alaska St
o 12th Ave S and S Main St
o 10th Ave S and S King St
o Aurora Ave N and N 128th St
o SW Holden St & Highland Park Way SW
o E Marginal Way S and S Dawson St
o 1st Ave NE and NE 105th St
o Aurora Ave N and N 97th St
o E Jefferson St and Terry Ave
o 12th Ave E and E Marion St
o 12th Ave E and E Spring St
o 20th Ave NW and Leary Way NW
For any questions please contact: traffic.signals@seattle.gov