And the Sightline Institute points out that it's happened after voters could legally smoke pot:

Sightline_WA-fatalities.png
  • Sightline Institute
One of the often-overlooked benefits of declining driving, particularly among the young, has been a rapid reduction in car crash deaths over the past decade. And those safety improvements have probably been helped by falling sales of super-sized pickups and SUVs, along with other promising automotive technology trends.

But during last year’s debate over marijuana legalization in Washington, I heard quite a bit of concern that permissive marijuana laws would reverse the recent declines in crash fatalities. I recall chatting with a well-meaning tow truck driver—a guy who’d seen the aftermath of a lot of terrible crashes—and he was convinced that legalizing pot would just mean more dead kids. Being a parent myself, I found it easy to understand that perspective. Despite a long-term decline in alcohol-related crashes in the state, drunk driving is still a very serious problem—and I can certainly relate to the fear that legalizing another intoxicating substance would boost car crash deaths.

So far, though, the opposite has been true: crash fatalities in the first part of the year seem to have fallen to a new low.

This is a tiny sample size from only four months, and the Sightline Institute acknowledges these are preliminary numbers, but if the trend continues through future years in Washington and Colorado, which also legalized pot, these sort of findings may help debunk claims that pot legalization causes more highway fatalities. (That argument was used heavily to stop previous legalization initiatives in California and Nevada.) But to the larger point—larger than pot—I'm just glad fewer people are dying on our roadways.