Traffic Calming

City of Lynnwood has a mature and successful Neighborhood Traffic Calming Program.

The program seeks resolutions for speeding complaints. We first collect vehicle volume and speed data; usually over a full week. We then find the 85th percentile speed from that data. In Washington State law, the speed from the 85th percentile is the safe speed for that section of roadway. It can be different compared to the posted speed limit. State law asserts that 85 out of every 100 motorists are law-abiding and safe drivers. Depending on the area, when we find that the 85th percentile speed from collected data is more than the posted speed limit, the street segment may qualify for either raising the posted speed limit or installing traffic calming measures. In most cases the speed limit is not raised, due to being a residential area or school zone. Lynnwood engineers look for reasons motorists may be elevating their velocity. Long, straight, wide, downhill lanes with little or no on-street parking tend to produce higher 85th percentile speeds. If this is the condition, we put the street segment on a waiting list for a traffic calming project. Timing of the project is subject to backlog and funding.

Residents submitting complaints of speeding vehicles might wonder about the 15th percentile drivers. They are the aggressive drivers with intentional (late to an appointment) or conditioned habits of speed while driving. They are also the distracted or impaired drivers; texting, medicated, marijuana or alcohol. Lynnwood’s traffic calming program cannot design to stop the 15th percentile drivers. An example to stop behavior of an impaired driver would be installing guard-rails on both sides of all lanes. The expense alone for projects like this make it impossible.

15th percentile drivers will be present after a traffic calming project. It is most likely the 15th percentile drivers that motivate residents to submit a complaint about speeding in a neighborhood. If after collecting data the 85th percentile speed is close to the posted speed limit, we will notify Police requesting speed enforcement. We would not add the street to the list for traffic calming projects.


Questions? Contact the Traffic Department at 425-670-5234 or