1. Denver-Aurora, Colo.
AP Photo/David Zalubowski, file
Denver’s public transit includes bus and light rail lines, as well as an airport shuttle service. The MallRide bus lines also transport passengers over the city’s mile-long 16th Street Mall for free, seven days a week. The city is also undertaking a multi-billion-dollar expansion of its transit system to increase light rail, commuter rail, and bus rapid transit lines.