You're asking good questions, and perhaps in time (and with more data), we can better account for what's going on.

One thing to always keep in mind when you look at traffic incident stats is that certain things change over time.

For example, additional measures to make roads safer, better technology in vehicles, more effective emergency medicine, and new laws are constantly been put in place to reduce accidents (and fatalities).

Why do I mention this? Because we could very well have more DUI drivers on the road who may have THC levels high enough to be legitimately impaired, but these other factors are balancing out the risk of those impairments.

This could explain why we're catching more DUI drivers, but seeing fewer DUI crashes or fatalities.