To illustrate this point, the report compares the components of the travel time of typical commuters in Chicago and Charlotte. The average Charlotte commuter spends an average of 48 minutes on the road—38.4 minutes in free-flowing traffic and another 9.6 minutes in traffic delays. The average Chicago commuter spends just 32.6 minutes in total travel time—22.8 minutes in free-flowing traffic and 9.8 minutes in delays. The reason for the difference boils down to a simple factor: Chicagoans live closer to where they work, with an average commute of 13.5 miles, compared to an average commute of 19 miles for residents in Charlotte.

The key lies in urban form, the report concludes. Denser metros enable more commuters to live closer to where they work, while more sprawling regions cause residents to endure longer trips. The report estimates that if "the top 50 metros followed suit with Chicago" residents would drive "about 40 billion fewer miles per year and use two billion fewer gallons of fuel," and generate a total cost savings of $31 billion per year.

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