An A Line train rests at the Denver International Airport platform on the line's opening day, Friday, April 22, 2016.

(Nathan Heffel/CPR News)

Posted 7:30 a.m. | Updated 3:00 p.m.

Some 30 years after work began to replace the old Stapleton Airport, Friday marked the final milestone in efforts to build a world-class airport for Denver.

The A Line train, which carried passengers between Denver International Airport and downtown in 37 minutes for $9, is now open.

“We used to compete with Dallas and Chicago," said Kim Day, DIA’s CEO. "We now compete with Zurich and Amsterdam and Incheon. And this train is one of the game changers that put us there.”

Denver Mayor Michael Hancock says the success of the new line will be dependent on a number of things, including interstate traffic congestion around the airport.

“Certainly a year from now, two years from now we’ll look at how we’ve been able to abate some of that congestion," Hancock said. "We’ll look and see how people are using the line to get to and from the airport, as well as the R line coming in out of Aurora."

RTD expects 18,000 people a day will ride the $1.2 billion train, and that means some disruptions. Bus routes along the line have been adjusted. And what happens to shuttle and taxi companies if their customers hop on the train?

“We would much rather be sustainable, get people out of their cars and onto the train," Day said. "It’s a win-win for everybody.”

But one company, Super Shuttle, which provides door-to-terminal bus service, is feeling the heat. It just cut its rates up to 25 percent. Company officials say their shuttle is the most economical way to get to the airport.

But that depends. A trip on the train costs $9. A non-stop Super Shuttle van with up to three passengers costs around $64 -- even with the reduced rate.

Others don't seem to be concerned. Some taxi and Uber drivers are confident the train won't cause a big drop in customers. A large private parking provider doesn't seem worried either. Eddie Weld, a bus driver at Wally Park, said train travel doesn't work for everyone.

"For the guy with three kids, four kids with a lot of luggage ... it’s kind of hard for them," Weld said.

Weld thinks Wally Park’s customers are pretty loyal. But at least one of them is tempted by the train. Laura Skien of Denver is on her way to see her husband in Chicago. While she typically drives to the airport and pays to park, the train has her reconsidering her options.

"We’ve been doing this for years," she said. "It’d be nice to change though."

RTD’s new general manager Dave Genova says the new line should be able to coexist with other transportation and parking options, including the numerous RTD bus lines that travel to and from the airport.

“Everytime we open a major corridor, you know, our service plan changes quite a bit as far as bus connections and routes," he said. "But we’re very cautious and when we re-design those to make sure that we’re serving the community the best we can.”

RTD says the A Line will bring the biggest change in service since 2006. Dozens of bus routes are being added or extended and six routes, including the sky bus between Denver and DIA have been discontinued.

While the A line is the first commuter line in Colorado opening this year, it’s not the last. Three other lines will open by year's end. However, commuter rail service to Boulder and Longmont and the completion of FasTracks remains decades away.