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DENVER (KDVR) — Since its debut five years ago, the RTD University of Colorado A Line has shuttled millions to Denver International Airport. It hasn’t been a cheap or smooth ride.

The University of Colorado A Line, or the A Line, has lived through hard times for public transit in its short years.

RTD ridership was already plummeting around Denver in 2019, a year before the pandemic hit. Internal reports say RTD failed to hit its reliability and safety goals, meanwhile raising fares to the most expensive rate of any comparably-sized American city.

A year later, the pandemic gutted RTD ridership by as much as 90%.

Against this backdrop, the A Line now commands arguably the largest role in RTD’s budget. Only the 16th Street Mall rail has more boardings.

A fifth of RTD’s rail boardings were on the A Line in 2019, the most recent figures available. It took only three years to double to this point. In 2016, it accounted for only 10% of boardings. By 2019, it accounted for 17.5% of RTD rail boardings.

Earnings from fares went up along with the ridership. By 2019, 36% of RTD’s fares come from the A Line alone.

It takes more than 17% of RTD’s budget, however. According to service figures, the A line is the RTD’s most expensive rail.

Ridership doubled since opening, but expense rose even more quickly.

In the first three years it was open, the A line’s operations expenses quadrupled. In 2016, the airport commuter line had a $44.8 million operations cost. By 2019, that had grown to $171.4 million.

That boost in operating cost made it the single largest percentage of the RTD’s total operating budget.

In 2016, the A line took 17% of the RTD operating budget. Three years later, it took 38% – four times as much of the operations expenses as the next most expensive rail line, the E line.

This means the airport line has taken up its share more of taxes, which fund the majority or RTD’s budget. Fares, by contrast, paid for 6% of RTD’s cost in 2019.

Every rider that boards an RTD vehicle pays a fare and also costs an additional amount of money from other sources. The A-line costs the most per person to subsidize than any other line except the G line, which carries only a fraction of the people a fraction of the distance as the airport line.