San Francisco residents will have their their first opportunity Tuesday to weigh in on a new study looking at the possibility of removing a 1.2-mile stretch of Interstate 280 in the city and reconfiguring the future route of high-speed rail and Caltrain into the Transbay Transit Center.

The “Rail Yard Alternatives and I-280 Boulevard Feasibility Study” — known as the RAB — is a multiagency analysis of transportation and land use alternatives South of Market, in Mission Bay, Showplace Square and lower Potrero Hill. The first part of the study — which will be unveiled Tuesday night at the Potrero Hill Recreation Center — took a year to produce. Planners expect it will take another two years to finish the rest of the document.

They argue it doesn’t make sense to invest billions of dollars to extend Caltrain and bring high-speed rail service to downtown San Francisco using antiquated infrastructure — an elevated freeway, a half-mile-long rail yard, street-level commuter rail tracks — that are vestiges of the area’s industrial past.

Moving or shrinking the train yard and turning I-280 into surface a boulevard — similar to the Embarcadero and Octavia Boulevard — would knit SoMa together with neighborhoods like Potrero Hill, Mission Bay and the Dogpatch. It could also free up 25 acres of land for development, which could help pay for transportation improvements.

Menu of options

Susan Gygi, a senior planner and engineer with the city, said all of the components in the study have been looked at separately over the last 25 years “but never holistically.” She said the intention is to create a menu of options ranging from figuring out the best location for Caltrain stations to the best route for trains coming into the city.

One of the top objectives of the study will be looking at the feasibility of boring a train tunnel under 16th Street. The current plan calls for “trenching” 16th Street and Mission Bay Drive, the only two streets that connect Mission Bay with surrounding neighborhoods, so that trains would be able to travel on top. But submerging those streets would create grim and potentially dangerous thoroughfares for pedestrians and cyclists, said Gillian Gillett, director of transportation policy for the city.

“Those two streets will be depressed at great expense, resulting in an urban form that is invasive and hostile,” Gillett said. “We don’t want our streets to get trenched. We did that to Cesar Chavez Street, and it doesn’t create a good environment.”

The study will review construction methods and rail alignments, including the possibility of moving the Caltrain station at Fourth and Townsend streets to Third Street, between AT&T Park and the planned Warriors arena. It will also look at the potential of creating a loop track at the Transbay Transit Center, rather than a stub, where trains have to end and exit on the same track. A loop track would increase the station’s overall capacity.

The Fourth and King rail yard now provides train storage, maintenance and operations activities for Caltrain. Modifying or relocating some of these activities would free up land for everything from parks to affordable housing to office buildings.

Funding falls short

The study comes as the Transbay Joint Powers Authority is scrambling to bridge a gap needed to finance construction of the $2.4 billion transit center, which is set to open in 2017. Phase two, the 1.3 mile downtown rail extension, will cost $4 billion and is largely unfunded. Meanwhile, Caltrain is $433 million short for its $1.7 billion electrification project, which is scheduled to be done by 2020. That number would be cut by $125 million under President Obama’s proposed budget.

Given the funding gaps, Gillett dismissed the criticism that a three-year study could slow down efforts to bring Caltrain and high-speed rail downtown. The lack of transportation planning has led to a situation where thousands of units of housing are being developed in areas like Potrero Hill and the Dogpatch, which are poorly served by transit.

“One of the reasons we are in the soup we are in is that development and transportation improvements have not been happening at the same time,” Gillett said. “If you are going to invest in this big seismic shift from diesel to electric, which we have got to do, you also have to look at all the stations. Are the tracks in the right place? Are the stations in the right place so that we can create real connections to other systems?”

J.K. Dineen is a San Francisco Chronicle staff writer. Email: jdineen@sfchronicle.com Twitter: @sfjkdineen

Public meeting

The presentation will take place from 6 to 8 p.m. at the Potrero Hill Recreation Center, 801 Arkansas St. in San Francisco.