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35th Avenue SW and SW Roxbury Street – Early Results are In!

SDOT would like to thank the West Seattle community and travelers for their patience during the rechannelization construction projects along the 35th Avenue SW and SW Roxbury Street over the past month. Crews finished installing the new designs in late September and have been refining signal timing since then. The construction is mostly complete on both projects, though there are some minor adjustments to be made over the next few weeks.

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SDOT worked with the community, King County Metro, emergency services, and local businesses to develop a plan that addresses the combined needs to make 35th Ave SW and SW Roxbury St safer for everyone. Collisions related to speeding and turning vehicles were issues along both corridors. Rechannelization is a low-cost engineering solution that addresses these collision issues. SDOT is excited to share some of the early results!

Reconfiguring a street from four lanes to three lanes is a significant change. We removed one lane in each direction and added a center two-way left-turn lane introducing a more organized and predictable street. People driving straight or making turns now have dedicated lanes. Pairing these changes with new signal timings has made little impact to travel times while significantly improving safety for drivers, transit riders, bicyclists and pedestrians alike.

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The project team has been monitoring the revised segments of 35th Avenue SW and SW Roxbury Street on a daily basis. We’ve also collected data in an effort to obtain preliminary insights into the effects of the recent changes.

To date, we’ve seen no change in volumes on 35th Avenue SW or SW Roxbury Street. Daily traffic volumes on these streets remain within the same range as pre-project volumes. During our public outreach process, some people commented that they were concerned about drivers diverting to nearby residential streets after the channelization changes. We’ve received no reports of diversions from residents and our volume data does not indicate diversions to residential streets. However, we will continue to keep an eye on this issue moving forward.

Our first look at vehicle speeds on 35th Avenue SW is encouraging. The street once commonly referred to as “I-35” in the neighborhood no longer sees the majority of drivers pushing speeds up to 40 miles per hour. Instead, most drivers now travel around 34 to 35 miles per hour. This is a significant improvement but we’d like to see drivers traveling at lower speeds which are closer to the new posted speed limit of 30 miles per hour. We will expand our speed data collection efforts in October and November and hope to see lower speeds as drivers adjust to the new conditions.

There’s no doubt that these corridors feel different than they used to, especially during the afternoon commute when traffic volumes are highest. With just one general purpose travel lane in each direction, vehicle queueing at signalized intersections is more substantial during the afternoon/evening commute period. However, longer signal cycles effectively mitigate the queues and vehicles are able to clear intersections in just one green phase. Occasionally, emergency response vehicles such as police and fire will preempt signals at SW Holden Street, so it can take up to two signal cycles to clear the intersection when traffic volumes are high.

Again, the corridor feels different but vehicle and transit travel times have been minimally impacted. During community outreach, we mentioned that traffic modeling projected delays on 35th Avenue SW of one-to-two minutes with a maximum delay of 2.5 minutes during the afternoon rush hour. Our travel time data, based on driving the 35th corridor dozens of times during peak hours, show that our models were a bit conservative:


Travel Times in a Car (35th Ave SW from SW Roxbury St to SW Morgan St)
Before Rechannelization After Rechannelization Difference
AM 4 mins 41 secs 4 mins 39 secs – 2 secs
PM 3 mins 50 secs 5 mins 22 secs + 1 min 32 secs
AM 4 mins 26 secs 4 mins 42 secs + 16 secs
PM 5 mins 22 secs 5 mins 36 secs + 14 secs


During the off-peak hours, travel times are unchanged and both corridors flow very well. Even the morning peak hour commute is functioning much as it did pre-project. The afternoon commute is the busiest time of day on both 35th Avenue SW and SW Roxbury Street. Drive times during the afternoon commute southbound on 35th have ranged from a high of 6 minutes and 49 seconds (1 minute and 13 seconds slower than pre-project travel times) to a low of 4 minutes and 53 seconds (43 seconds faster than pre-project travel times). Travel times northbound on 35th during the afternoon commute have been consistently running 1 to 1.5 minutes slower than pre-project travel times.

On SW Roxbury Street, travel times have remained steady when compared to pre-project data.

Bus travel times are also looking good. SDOT teams have been riding the bus (21/21X) regularly to collect data. As demonstrated in the chart below, travel times have been fairly close to pre-project levels. We have also been encouraged by the fact that it’s taking transit operators an average of 2.5 seconds to re-enter traffic after loading and/or unloading passengers at bus stops. Clearly West Seattle has done a great job of yielding to buses which greatly helps our transit system move thousands of people per day. Thank you!


Travel Times on a Bus (35th Ave SW from SW Roxbury St to SW Morgan St)
Before Rechannelization After Rechannelization Difference
AM 9 mins 7 secs 8 mins 55 secs – 12 secs
PM 5 mins 22 secs 5 mins 56 secs + 34 secs
AM 5 mins 22 secs 5 mins 56 secs +34 secs
PM 10 mins 43 secs 9 mins 28 secs – 1 mins 15 secs


Data and all materials from our public meetings can be found on our website. Click here to learn more about Roxbury and here [] for more information about 35th Avenue SW. As always, we encourage you to send comments, observations and suggestions to SDOT at or 206-684-9255. SDOT has collected an immense amount of data for these projects and will continue to monitor these corridors in perpetuity. In the near term, we’re watching intersection performance closely to determine if signal timing changes or turn phases are needed to achieve our safety goals. We’ll continue to collect data over the next year, and, in October 2016, we will produce a before and after evaluation of the project. This will include thorough analysis of travel times, collisions, volumes and speeds.