One of the major concern surrounding pot legalization and decriminalization has been the issue of impaired drivers. Colorado's Senate had to decide last night if they wanted to pass a bill that would make it illegal to drive with more than 5 nanograms of THC per liter of blood in your system. They rejected the bill, for now.
The issue here was that they didn't have enough research. This law is starting a fire in a hot area of dispute inside and outside the marijuana community. Stoners have long had their own ideas about driving while high. Some will tell you they never do it because it feels too dangerous, and others say that they drive better stoned. Drive better stoned? That's a sentiment that many are likely to dispute.
It brings up an important issue though. Is all intoxication impairment, and do drivers under the influence of marijuana cause accidents. The fact is that we don't really know, and that's why the bill failed. The senate decided they need more research before they move forward with a law like this.
This is by no means a simple law to enact. Marijuana unlike alcohol affects users in far more unpredictable ways. Depending on exposure two people might have completely different reactions to the same dose.
"... [Sen. Shawn] Mitchell said... Echoing the concerns of a number of lawmakers, Sen. Morgan Carroll, D-Aurora, said she thinks the research is inconclusive about how much THC definitively causes impairment, meaning a 5-nanogram limit might snare sober drivers while allowing stoned ones to go free." - DenverPost.com
The world will be looking to Colorado to set the precedent for laws of this type.