All Colorado roadways have a speed limit. And it's not new.
"In 1652, the colony of New Amsterdam (now New York) issued a decree stating that “[N]o wagons, carts or sleighs shall be run, rode or driven at a gallop” at the risk of incurring a fine starting at “two pounds Flemish,” or about $150 in today’s currency." -History.com Editors
Speed limits are set by each state for the safety of all people on or around the roads: people in your car, people in all other vehicles around you, people living, working, or crossing the street. Science establishes that the safest speed on any roadway is the speed at which 85 percent of motorists travel. That's how we end up with a speed limit of 75 mph on highways being considered as safe. The makeup and location of the road also contributes to the speed limit. A narrow mountain road will have a limit closer to 20 mph, while a two-lane mountain highway will have a limit of 55 mph.