Below is an outline of the traffic calming procedure.
Tier 1 Traffic Calming:
1. Collect and analyze speed data
2. Is the 85th percentile speed ≥ the speed limit + 5 mph?
The 85th percentile speed is the speed at or below which 85 percent of all drivers are observed to travel under free flow conditions. The City considers excessive speeding if this speed is 5 mph over the speed limit.
- Yes, then Tier 1 Traffic calming treatments are installed.
- No, then speeding referred to Renton Police Department and no traffic calming is installed. Radar trailer(s) deployed; residents may request radar trailers at any time.
3. After at least one year, speed data collection and analysis are repeated.
- If speeding persists, consider Tier 2 Traffic Calming Treatments, or large-scale project in TIP.
- If speeding does not persist, existing traffic calming treatment remains, and no other action taken.
Driver Feedback Sign Rotation:
Driver Feedback signs are a Tier 1 traffic calming treatment that use radar to display the driver’s speed and the message “SLOW DOWN” if going too fast. A speed limit sign is also posted with the Driver Feedback sign.
1. Installed for 3 months, then rotated to other locations throughout the city.
2. Reinstalled after 9 – 12 months.
3. Speed data collected after 2nd installation to determine if Tier 2 traffic calming treatments are needed.
- If speeding continues, Tier 2 traffic calming treatments may be considered.
Tier 2 Traffic Calming:
1. Tier 1 procedure completed after a year and speeding persists.
2. Appropriate/feasible Tier 2 traffic calming treatment selected.
3. Project is ranked among all current projects.
- Ranking is based on 85th percentile Speed, number of speeders, school walk route or school bus stop, pedestrian activity level, and crash history.
4. Survey letters mailed to residents for support.
- If >65% support traffic calming treatment, then project moves forward.
- If <65% support traffic calming treatment, then Tier 1 traffic calming treatments will remain. Alternative designs may be investigated, and residents will be surveyed again.
5. Implement design and construction.
6. Traffic calming procedure concluded by a before and after traffic study.