DENVER—As Denver moves forward with a $7.4 billion expansion of its rail system, the city is looking to rectify what some see as a flaw in the original concept.

The dilemma is how to encourage the development of dense, walkable villages around stations so people don't have to drive to use the system.

After the system opened in 1994, planners built parking lots and garages around many of its stations to cater to commuters. That strategy put parking on land that would have been ideal for stores, apartment buildings and squares catering to riders living adjacent to the stops.

As a result, there has been little of that kind of development around the stations to change the area's car-dependent culture, and riders commute to the stations from up to 20 miles away.

"Once you put in a parking structure, it's difficult to move it," says Bill Sirois, senior planning manager at the Regional Transportation District in Denver.