This more southerly route does not use Toll roads. It usually takes 50-70 min, about 10-15 minutes longer than the toll route. Distance is about 40 miles.
This more northerly route uses a toll road and takes 40-55 min. Total toll is about $8. You will be automatically billed through your license plate number (rental cars included). Distance is about 40 miles.
SuperShuttle Boulder 303 227-0000 or 800-258-3826. Take the train from the gate areas to the terminal and proceed up the escalators to Level 5 / Baggage Claim. Claim your luggage, and then proceed directly to the SuperShuttle Boulder counter (open daily 7:00 AM - 11:00 PM) across from the water feature under the Ground Transportation signs. Shuttles leave every hour, 7days a week. There are more frequent departures on the ½ hour during some busy afternoons and evening hours. Trip time can be as little as 65 minutes if there are few hotel stops before yours. One-way fare to some hotels is about $25. You can be taken to any address in town, including campus, for an extra $6 or so. You may make reservations from Boulder to the airport, but not from airport to Boulder.
The Denver RTD AB Skyride bus runs from DIA to the CU campus. Single tickets cost $12 (exact change required). The bus stops within a quarter mile of Guggenheim Hall skyRide to DIA 303 299-6000 then type 1-2-1. The bus is cheaper than the shuttle but also less convenient and slower. Check departure times at the RTD skyRide counter, inside door 506. Use Route "AB" to get to Boulder. Buses leave for Boulder every hour or so between 6:20 a.m. and 11:25 p.m. Trip time is 90 minutes or more, with several stops in Boulder before the Boulder Transit Center downtown.
Because of the long distance to Boulder, cab service is expensive. Expect to pay in excess of $75. That's three times the shuttle van cost.