Hardly surprising - anything that interferes with alertness and decision making is going to have an effect on driving and other statistics.
Other than for prescribed medical use Cannabis really is a silly thing to legalise, unless of course you are trying to subdue your population.

Just 2 *hugely* important +ve results from legalizing cannabis:- 1/ The authorities immediately lose one very robust and very overused power to stop and search people unnecessarily (certainly from a UK perspective - and if you are wondering what the connection is between the US and the UK in this context, it is simply that what happens in the US usually happens over here a few years later). No longer having this power would suddenly remove a very significant cause of friction between the police and, particularly, the Afro-Caribbean community. What hope have young British Afro-Caribbeans of growing up with an open attitude towards the police when their very first (and probably many subsequent) interactions with the police is being stopped and searched on the basis of 'suspicion of possession of cannabis'? 2/ The authorities can stop wasting vast sums of money on trying to enforce anti-cannabis legislation and concentrate instead on much more serious matters, including those that claim the lives to thousands every year (unlike cannabis use).

Brian M, "....unless you are trying to subdue your population." This is where the renewed interest in possible Russian and Chinese influence, working through the social websites etc, comes from. As you say the influence of pot on a habituated individual probably is small, and difficult to measure unless a severe mental condition results, but the theory is that in the concealed warfare of this sort, all you need to do to win is to lessen the overall competence of the population. This idea has been misused of course, as in the view that the reasons for teaching the "New Maths" in the UK was a plot to lessen the development of logical and mathematical abilities of a typical UK child and so of adults too.

So, has there been a similar spike (and subsequent fall) in accidents around the home?

Disclaimer: I am not a pot smoker but I also do not believe self-impairment nor self-harm should be criminalized; there are plenty of laws criminalizing the downstream "effects" of being impaired.
1. " fatality increases seem to only be temporary" ...to the analyst maybe.. To the person (and his or her loved ones) getting mowed down by the stoned driver this "interesting revelation" is quite permanent.
2. Pot legalization is not a "progressive wave", it is a regressive one... In fact it was quite legal in the USA until 1937 when FDR outlawed it (among many other "Progressive wave" agenda items).
3. A review of local sheriff reports tells a much darker story. Reality is not always captured effectively with these reports: In this case these reports water down the impact by spreading the fatality spikes across a broad distribution.

The noted increase is "about one extra traffic fatality per million"! What's the normal variance in these kinds of data? What's the margin of error? And beside that, the increase is temporary. This is nothing; it's just feed for headlines. Even if the increase is real, it might just be the result of traffic from the harsh states into the more free states. On TOP of all that, compare this one per million to the offsetting count of people killed (and lives ruined) due to enforcement of this cruel war on a weed.

Say, @Brian - ya gotta keep the peasants distracted somehow!

I, for one, think that, marijuana should be legally treated like alcohol!

@clay Excellent points.

If you want to dumb down the population, this is the way to do it. Children's brain development has been found to be severely impaired by marijuana but politicians don't seem to care. If you know someone who has been using this stuff since childhood, you can easily tell how dull witted they have become.