So, the real question is — have things gotten worse. And reason would indicate, yes.
Before, you had just one legal intoxicant and one illegal. Now you have two legal intoxicants. Granted many people smoked it illegally but I argue that a lot more people are smoking it now because it is legal. Heck, there has probably even been a large influx of people to Colorado because pot is legal; people who would be more likely to smoke pot.
So, yes there would be more stoned people on the roads than before pot was legal. and so the incident of accidents would increase. Note: no doubt that there are people who are never counted — legally intoxicated drivers but never caught.
Feel free to answer the question instead of evading it.