It's not too surprising that lower speed limits contribute to safer roads. Research from the Insurance Institute for Highway Safety suggests this is also true for some city streets where people are already driving relatively slowly. 

The data behind this study comes from Seattle, Washington, lowering the speed limit on arterial roads in the downtown area to 25 miles per hour from 30 mph previously in November 2016. In addition, the city dropped the limit on residential streets to 20 mph from the previous 25 mph. 

The stats showed that for the arterial roads in downtown Seattle the likelihood of a crash resulting in an injury fell by 20 percent. For these streets outside of the city center, there was an 11 percent reduction, which the IIHS said was not statistically significant.

"These results illustrate the value of rethinking speed limits. Crashes still happened after Seattle’s changes, but they weren’t as dangerous," said IIHS President David Harkey about the study.

The IIHS researchers looked at three years of crash data for Seattle and three other cities in Washington that didn't change their speed limits. They found that the proportion of collisions with injuries dropped on the arterial roads in Seattle. Meanwhile, this figure increased in the other locations.

On the residential streets, there wasn't a significant change in the chances of a crash causing an injury. The IIHS researchers have two theories about the reason for this. A small sample size could be a factor. Or, since these roads are narrow and often have on-street parking on both sides, drivers might not go much faster than 20 mph regardless of the posted speed limit because it doesn't feel safe.

Research from the National Highway Traffic Safety Administration showed that traffic fatalities fell 0.2 percent from January through September 2022 versus the same period in 2021. The tiny drop happened as drivers covered 1.6 percent more miles than in the previous year's first nine months.

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