Very likely, and even if it were not the case you could still have a net decrease in DUIs with an increasing amount of marijuana DUIs.

I am pretty sure there have been some studies that show people under the influence of marijuana are less likely to drive than people under the influence of alcohol so it just depends on whether marijuana is replacing alcohol or not.

These driving while high statistics are pretty error prone. There is no marijuana breathalyzer. A blood test shows traces of THC in your body from up to 30 days ago. So if you get in an accident and get blood tested and it comes back positive, were you high at that moment? Or a week ago? Or a month ago?

I'm sure the technology will improve. In fact, a "marijuana breathalyzer" (using that term loosly because you would need something that can test for edibles too), is probably a pretty interesting product to bring to market