The use of Drug Recognition Experts in Marijuana DUI investigations is on the rise. Indeed, the numbers of officers with the enhanced training have proliferated over the last few years, influenced heavily by the changes in the laws related to recreational use of pot.
While training of any kind is certainly a good thing, it is important to not place too much reliance on the DRE. Certainly cops who go through the block of extra training and are certified as a DRE are better suited to evaluate a suspected drugged driver, however we must be careful to not place too much emphasis on their conclusions.
Recently, the Press Enterprise published an article discussing these issues. The article can be viewed here Attorney Matthew Ruff Quoted in DUI Marijuana Article.