Evaluating traffic safety projects

A person bicycling in the green protected bike lane, adjacent to a yellow and black bus platform and red Rose Lane for buses on SE Hawthorne Boulevard, east of Martin Luther King Jr Boulevard.
A collection of evaluation reports for various Portland Bureau of Transportation (PBOT) traffic safety projects organized by roadway reorganizations, speed limit reductions, and quick-builds, among others.
On this page

Every year, the Portland Bureau of Transportation (PBOT) makes improvements on Portland streets to make them safer. Some of this work has been tried and tested before. Some are newer innovations. Below are key takeaways and a series of evaluation reports on various projects, organized by type:

Roadway reorganizations 

Chart illustrating the average change in top-end speeding between five street segments -- reductions range from -67 to -81%.

PBOT reorganizes roads by changing lane configurations, restriping, and/or building new safety infrastructure. Fewer lanes and shorter crossings make it safer and easier for pedestrians and people biking to cross. Roadway space can also be repurposed to add or improve bike lanes, a center turn lane, add on-street parking, bus platforms, plant trees, treat storm water, build new sidewalks or widen existing ones, as well as a number of other uses depending on the project.  

The evaluations show that when PBOT repurposes a vehicle travel lane for other uses, travel speeds tend to go down. We also see a dramatic decrease in top-end speeding (10 mph or more over the speed limit). The projects evaluated here have had minimal impact to travel time, transit reliability, or overflow traffic spilling into nearby residential 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 culture of driving slower, and allow us to design streets for slower speeds.

The evaluations from Portland and other cities we've included here show how reducing the speed limit resulted in lower observed speeds and a more pronounced decrease in drivers travelling at high speeds.

Speed reduction evaluation reports (from newest to oldest):

Effects of lowering speed limits on crash severity in Seattle (2023) - from the Insurance Institute for Highway Safety (IIHS)

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 we can build in multiple locations to address the common causes of crashes.

Left-turn calming is one intervention that PBOT piloted in 2019 to help protect pedestrians. Hardening the centerline at certain intersections by adding rubber speed bumps or plastic or concrete barriers led to people slowing down while making left turns and substantially reduced the number of sharp, angled turns.

Quick-build intervention evaluation reports (from newest to oldest):

Other evaluation reports from Portland and other places