Trains taking passengers from Fort Worth to DFW International Airport could be in motion by 2018, now that the federal government has pledged to pay for nearly half of the $1 billion rail line.

This month, the Federal Transit Administration signed an agreement with the Fort Worth Transportation Authority, or The T, to provide a $499 million grant for the TEX Rail project. The other half is being paid for with local and state money, officials said.

Paul Ballard, chief executive officer of The T, said the rail line is critical for the long-term economic viability of the Fort Worth area.

"Business today is global, and as businesses look to where they would locate or relocate, one of the check-offs on their list is, does the city and the county have a rail connection to the airport?" Ballard said. "And there are businesses that if you don't have that connection, they move on to the next city."

The rail line will span nearly 27 miles, with nine stops in Fort Worth, North Richland Hills, Grapevine and DFW Airport. From the airport's Terminal B, passengers can move to Terminal A, where they can catch a train to Dallas via the Orange Line operated by Dallas Area Rapid Transit.

TEX Rail will share two stations with another commuter rail line, the Trinity Railway Express, which runs parallel to Interstate 30 from Dallas to Fort Worth. The T and DART operate that route together.

A map showing the TEX Rail route ((The T))

The T's new line is the western half of what is known as the Cotton Belt rail corridor. This year, the DART board approved plans to develop its portion, running from DFW Airport to Plano, in the next decade.

The decision was controversial because many in Dallas view the eastern Cotton Belt as a threat to a future subway line in downtown Dallas. DART voted this year to pursue both projects at the same time, choosing to take out debt for the Cotton Belt and apply for federal subsidies for the subway. Critics of the eastern Cotton Belt say the debt tied to the project will hurt DART's finances and compromise its ability to get the federal funds.

The western half of the Cotton Belt has also faced opposition. Colleyville residents and city officials voiced concerns that the line would bring noise and hurt property values, but they failed to derail the project.

The T has been actively working on the rail connection to the airport for a decade, Ballard said. Crews broke ground on the project this summer.

Money committed by the federal government will be disbursed in annual payments over four years, which must be approved annually by Congress when it reviews the budget.

Transit officials in North Texas praised the T's milestone.

"We're pleased that they're continuing to make progress on the project," DART spokesman Morgan Lyons said in an email.

Michael Morris, director of transportation for the North Central Texas Council of Governments, applauded the decision of federal officials to send more transit funding to Texas.

"The value of this action is not just in leveraging the federal funds with local contributions to advance a needed transportation project, but also in ... creating a system connection of rail transit from Fort Worth, through DFW Airport and on to Plano and other destinations in the DART system," Morris said by email.

Ballard said The T expects to open TEX Rail by the end of 2018. Ridership is estimated to start at 9,000 daily trips and reach 13,700 trips by 2035.

The T's ongoing challenge is identifying funds to expand its network, Ballard said. The transit agency has three member cities vs. DART's 13. The T collects about $70 million a year in sales tax revenue; DART raises half a billion.

One city that both DART and The T are wooing is Arlington. Both agencies will present to a transportation advisory committee in January.

Ballard said The T designed its most recent master plan to identify corridors it wants to invest in, without necessarily specifying the mode of transportation.

"It could include light rail, it could include streetcars or bus rapid transit or traditional bus services," he said. "We really keep an open mind."

Updated at 6 a.m. Wednesday: Revised to correct the name of Trinity Railway Express.