A stretch of the recently-reopened U.S. 36, looking west.

(Hart Van Denburg/CPR News)

RTD is offering free rides Monday on its newest bus line, the Denver-Boulder Flatiron Flyer.

The new bus line promises faster travel by using the express toll lane that opened on U.S. 36 in July.

The Flatiron service will consist of six routes –  some previous routes were dropped to decrease travel times. One-way fares will range from about $2.50 to $4.50. Riders have two options – express service with few stops between Denver and Boulder – and the all-station service.