The blanket law for Colorado is "reasonable and prudent", meaning don't go faster than is safe for conditions. In addition to that, limits for certain areas, unless otherwise posted, are:

  • Winding, narrow mountain highways and blind curves: 20 mph
  • Central business districts: 25 mph
  • Residential areas: 30 mph
  • Open mountain highways: 40 mph
  • Rural highways, including two lanes and four-lane divided: 55 mph, and up to 65 mph where posted
  • Rural Interstates: 65 mph, and up to 75 mph where posted
  • Home-rule cities can also adopt a blanket speed limit for the whole town, such as 25 mph, and it will be that unless otherwise posted.

Minimum speeds are required so that drivers are going fast enough such that they are not impeding or blocking the "normal and reasonable" flow of traffic. Colorado also has a "move right" law, saying that on a divided highway with a 65mph or higher speed limit, the left lane can only be used for passing when traffic is light enough.

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