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DENVER — A new study says Colorado drivers rank among the worst in the nation.

The QuoteWizard by Lending Tree study gives Colorado drivers a C- overall, using 100,000 Colorado insurance data quotes, Federal Highway Administration data and statistics from the National Association of Insurance Commissioners.

Some of the key findings include: millennials are the worst group of drivers in Colorado, Denver ranks the eighth-worst city in the country and Colorado Springs is ranked 16th.

The national rankings are based on accidents, speeding tickets, DUIs and citations.

The study says some of the worst-driving cities in Colorado include: Black Forest, Lafayette, Parker, Windsor and Johnstown. The best include: Pueblo, Durango, Fountain, Grand Junction and Boulder.

Colorado also had one of the highest spikes in car insurance rates, according to the study. It found a 27% increase in rates from 2012 to 2016, the highest increase in the country in that time.