A lot has been made of the $9 fare to get to and from Denver International Airport on RTD’s gleaming new A-Line. As Streetsblog reported a few weeks ago, it’s more expensive than airport rail in comparable American cities, but about the same as in San Francisco. CBS4 and ABC7 did similar stories more recently.

Why the high price?

For one, it’s a reflection of what it costs to operate the 24-mile airport line: about $42 million a year, according to an RTD spokesperson. RTD estimates that in its first full year of operation, even with the $9 price of a trip, the A-Line will pull in between $8 million and $16 million from fares. And since airport transit tends to serve business travelers and vacationers who can afford it, a higher fare makes sense.

But another factor in the A-Line’s fare is RTD’s decision to charge nothing or almost nothing for the 4,300 parking spaces along it. Parking costs transit agencies a fortune — about $15,000 to build each structured space in Denver [PDF]. Plus it will cost the transit agency up to $2 million annually to operate the A-Line’s park-and-rides (excluding the one at 61st and Peña, which is privately owned), according to RTD estimates. By charging so little for parking, RTD is effectively shifting these costs to passengers who don’t park and ride.

A new study from the Colorado Fiscal Institute actually recommends increasing the airport fare and charging for parking at the stations. That revenue would help fund discounted fares for low-income airport workers and transit-dependent riders system-wide.

The CFI authors say that RTD’s current policy of highly subsidized park-and-rides benefits more affluent car owners at the expense of transit-dependent riders:

Most low-income transit users would not be affected by parking costs. Approximately 25 percent of light rail riders and 53 percent of bus riders are transit-dependent and therefore do not have a need for parking. Most Park-n-Ride users ride the express and regional routes — 64 percent of express bus riders use parking and 48 percent of regional bus riders use parking, and tend to be higher income. Roughly 50 percent of express and regional bus riders live in households with more than $75,000 annual income. By contrast, only 10.2 percent of local bus riders use parking. Free parking at Park-n-Rides disproportionately benefits higher-income riders.

Transit advocates have been trying to lower fares for Denverites who depend on transit for a long time. Right now, 68 percent of low-income riders don’t get discounted rates, according to a Mile High Connects report, leaving many to pay full fares. That’s why a small group of protesters disrupted a celebration last week for the A-Line. “We need a way to get here to there,” they sang.

One way to help more people get from here to there on transit? Charge more for parking and stop subsidizing driving.