Law enforcement officials lack tools to detect cannabis-impaired driving as reliably as they can identify people who get behind the wheel drunk. Only a few states routinely test the blood of drivers involved in serious accidents for marijuana, and as a result, little is known about how cannabis use is affecting road safety. Complicating matters, state laws on cannabis-impaired driving are inconsistent and confusing, which has made them difficult for the police to enforce and for motorists to understand. In Colorado, scientists are pursuing a pair of studies they hope will help policymakers craft sensible, enforceable standards.  Read the article here.