If you want to travel the state, then you will need to rent a vehicle. Prices are the same as across the United States.
The state is roughly quarted by two major Interstates, the north-south running I-25 and the east-west running I-70. I-76 also enters the state in the Northeast from Nebraska. Outside of the Front Range, the rest of the state is traversed by small highways and county roads.
The major cities of the greater Denver area Denver, Aurora, Boulder, Lakewood, Littleton, Longmont, Broomfield are linked by bus transportation using RTD. Service south to Castle Rock and Colorado Springs is provided by FREX. The cost is very reasonable and the busses run regular schedules.
Taxis and shuttle services are also available throughout the state.
