The Portland Bureau of Transportation’s residential speed limit reduction from 25 to 20 mph, completed in 2019, has likely reduced driving speeds by small but significant amounts, according to an analysis conducted in partnership with Portland State University researchers.
Before and after data show that lower percentages of people drove above 25, 30, and 35 mph on streets subject to the speed limit reduction (see Table 1). These reductions in driving speed were found across a majority of the 58 locations analyzed in the study (see map below).
| Period | Greater than 25 mph | Greater than 30 mph | Greater than 35 mph |
|---|---|---|---|
| Before | 24.13% | 6.49% | 1.11% |
| After | 23.60% | 4.83% | 0.59% |
| Table 1. Percent of vehicles exceeding 25, 30 and 35 mph before and after speed limit reduction from 25 to 20 mph |
A statistical analysis of the data reveals sharp decreases in the probability of people driving faster than 25, 30, and 35 mph following the speed limit change (see Table 2).
| - | Greater than 25 mph | Greater than 30 mph | Greater than 35 mph |
|---|---|---|---|
| Estimated change in odds | -15.9% | -33.6% | -49.6% |
| Table 2. Estimated change in odds of observing vehicles exceeding 25, 30, and 35 mph after speed limit reduction |
Portland State University researchers write that the reductions in speeds are “noteworthy” due to “the link to crash severity for vulnerable users.” Studies have found that even small reductions in speed can have large safety benefits, especially for pedestrians.
Other findings from Portland’s study: Speeds tended to be higher on Wednesday, Thursday, and Friday relative to other days, on wider streets, and on streets with better pavement condition.
About three-fourths of Portland streets have 20 mph speed limits (see chart below). A citywide map of current speed limits is available here.