In Colorado, like in all U.S. states, it is illegal to drive while under the influence of alcohol or another substance that impairs you. One piece of information that is largely misunderstood is the blood alcohol content limit, which is currently set at .08%.
In Colorado, DUIs are handled a little bit differently than in other states. To start with, an automatic DUI is assumed if a driver's blood alcohol content is .08% or higher. This would be charged as a DUI.