Evaluating Safety Efforts

A chart showing the decrease in top end speeding for five projects
Aggregating evaluation reports of traffic safety projects.

Every year, the Portland Bureau of Transportation makes many changes on Portland's streets in an effort to improve safety. Some of the efforts are tried and tested while others are new attempts and innovations.

Below are some key takeaways and a series of evaluation reports. The evaluations included here fall into a few categories

Roadway Reorganization 

PBOT implements roadway reorganizations for a number of reasons. Fewer lanes and shorter crossing distances make it safer and easier to cross the street. The space can be repurposed to add or improve bike lanes, a center turn lane, on street parking, bus platforms, space to plant trees, treat storm water,  build or widen sidewalks, or a number of other sues depending on the project context.  

The evaluations show that when PBOT repurposes a vehicle travel lane for other uses, travel speeds tend to go down, with drastic decreases for top end speeding (10 mph or more over the speed limit). The projects evaluated have had minimal impacts on travel time, TriMet travel time, and traffic on nearby neighborhood streets.

Roadway reorganization evaluation reports (from newest to oldest)

Speed Limit Reduction

Setting safe speed limits has a number of important benefits aside from legally requiring people to drive slower. Consistent safe speeds limits result in lower driving speeds, promote a message of driving slower, and allow us to design our streets for slower speeds.

The evaluations in Portland and else were show that reducing the speed limit resulted in slightly but significantly lower observed speeds and a more pronounced decrease of drivers travelling at high speeds.

Speed reduction evaluation reports (from newest to oldest)

Lowering the speed limit from 30 to 25 mph in Boston: effects on vehicle speeds (2020) - from IIHS

Quick Build Interventions

To address the many needs across the city more quickly, PBOT is consistently exploring small and cheap interventions that can be implemented in many locations to address common crash causes.

Left turn calming is one intervention that PBOT piloted in 2019. Hardening the centerline at certain intersections by adding rubber speed bumps or plastic or concrete barriers led to lower speeds while making a left turn and substantially reduced the numbers of sharp turns.

Quick build intervention evaluation reports (from newest to oldest)

Other evaluation reports from Portland and other places


Leeor Schweitzer

Safe Streets Project Development and Policy