They were lower in the past.
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NHTSA contradicts you =>
Roadway deaths fall nearly 25 percent in a decade, fatality rates at a historic low
Dec 19, 2014
WASHINGTON – The U.S. Department of Transportation's National Highway Traffic Safety Administration (NHTSA) today released the 2013 Fatality Analysis Reporting System (FARS) data that shows a 3.1 percent decrease from the previous year and a nearly 25 percent decline in overall highway deaths since 2004. In 2013, 32,719 people died in traffic crashes. The estimated number of people injured in crashes also declined by 2.1 percent.
http://www.nhtsa.gov/About+NHTSA/Press+Releases/2014/traffic-deaths-decline-in-2013
Roadway deaths fall nearly 25 percent in a decade, fatality rates at a historic low
You don't remember that you were talking about Colorado, Washington, and Oregon? Colorado highway deaths were lower in the past.
What does it matter that Highway deaths may have declined in non Legal marijuana states? It has no bearing on the effect of legality in Colorado, regarding which it is too soon to assert any "effect".