I think drug recognition experts are a useful tool, but that has to do more with the per se limits.
Let me answer the other part of your question first. In terms of recognition, these would be the front-line officers. The only way that a driver would come in contact with a drug recognition expert is if the front-line officers had reason to suspect that they were impaired by drugs, otherwise they wouldn't come in contact with the drug recognition expert.
Who we found are failing to identify drug-impaired drivers are the front-line officers. I think there are levels of impairment, just like there are levels of drunkenness. Someone can be a little impaired, enough that they're distracted more easily. Maybe their coordination is a little bit off and they're at a higher risk of crashing, but they're not so impaired that it's easy to pick up. It's similar to the notion that you don't have to be a staggering drunk to have an increased risk of crashing. It's the front-line officers who weren't detecting these people, and the front-line officers I think would be the ones who would be using the screening devices as well.
In terms of drug recognition experts, they definitely have their place, and I think it's possible for people who have used multiple drugs to be impaired while under a per se limit. You want to be able to detect that impairment, but it's just such a lengthy and difficult process that I think it acts as a barrier to convicting someone of impairment. I think they have their place, but it's not the perfect answer.