Houston could have two light rail lines running to Hobby Airport after all, provided they share a lot of track.

After saying the potential $1.8 billion investment to take both the Green and Purple lines to the airport was too costly, Metropolitan Transit Authority board members on Thursday reacted positively to an alternate plan to extend both lines to a common point, then having them share a single track in each direction the rest of the way to the airport.

“This is the alternative that makes the most sense,” Metro board member Jim Robinson said. “It is far less expensive than running two different lines out there.”

A preliminary analysis estimates the extensions and the combined line would cost about $1.1 billion, and carry a similar number of daily riders as estimates for separate extensions of the Green and Purple lines — about 6,600 daily trips.

Though ridership is comparable or less than a handful of Houston bus routes, community groups and elected officials made rail to Hobby a priority when Metro started exploring future improvements. Transit officials, however, scaled back some of the plans when even some transit supporters bristled at spending nearly one-quarter of the region’s $7.5 billion long-term investment on trains to one airport.

At no time was rail off the table, however, officials said.

"There is overwhelming support for a line to Hobby," Metro Chairwoman Carrin Patman said, citing the 2,400 responses transit officials received at dozens of community meetings. Likewise, she said, more than half of the respondents also think Metro should run rail to Bush Intercontinental Airport.

LESS LIGHT RAIL: Metro scaling back future transit plans to one train to Hobby airport

The demand for service along the Green Line in east Houston and Purple Line through the Third Ward and southeast Houston was so strong, Metro pressed for both lines to avoid alienating supporters of either route. Those residents will be crucial supporters if Metro successfully convinces voters to support its long-term plans in November.

If it is included in the plan Metro takes to voters, the combined Hobby line would require much more study, though officials debuted a preliminary scenario Thursday: Metro would extend the Green Line along Harrisburg and then turn south and follow 75th Street and Woodridge to Gulfgate Mall, then use Telephone Road to travel south to Long Drive, where it would meet the Purple Line extension.

The Purple Line would make the trip from Palm Center Transit Center along Long Drive. Both lines would continue down Telephone and then along Airport Boulevard to somewhere at or near Hobby’s passenger terminal.

From downtown Houston, where the rail lines cross at the Central Station Main station, travel time to Hobby would be about 40 minutes along both routes, according to Metro estimates.

Sharing tracks is not a novel idea along the routes. Both share tracks in the central business district along Capitol and Rusk, splitting at BBVA Compass Stadium in EaDo.

The shared line and extensions have benefits and risks. Even as many remained supportive of light rail to the airport, community groups and elected officials urged Metro to make sure the Green Line did not use Broadway as a route southwest of Interstate 45. City and neighborhood officials redesigned the Broadway median as part of improvement efforts prior to Houston hosting Super Bowl LI in 2017, and balked at the idea of ripping up in a few years for a rail line.

LONG-TERM TRANSIT VISION: Metro plans mix of transit to meet differing Houston-area demands

As a result, the route along 75th Street and Telephone drew praise from officials with the Hobby Area District.

“The ridership there, I predict, would be phenomenal,” district board member Ann Collum told Metro officials.

The line could also provide a key link between the terminal and car rental lots, said Metro board member Sanjay Ramabhadran.

“It becomes an airport amenity,” he said, urging Metro staff to explore a partnership with Hobby leadership.

Many technical details of the light rail plan, however, remain unresolved, especially along the Purple Line. Numerous freight railroad tracks and major streets are knotted where the line would cross Loop 610. Former industrial properties along the route could pose environmental challenges.

Plus, though both 75th Street and Long Drive have medians, further street widening and construction could dramatically affect area businesses, something that dogged construction of the Green Line along Harrisburg from 2011 to its completion in 2017.

Despite uncertainties, many believe building rail to Hobby is inevitable as part of long-term expectations that travelers will demand.

“The idea is to serve the (George R. Brown) Convention Center,” Patman said at one point during discussions of the proposal, citing the need to cater to Houston visitors headed downtown.

dug.begley@chron.com