It's a bold idea, discussed for years behind closed doors and recently announced in a strangely understated and pro-growth way: Tear down the last mile of Interstate 280 and replace it with an wide boulevard – reminiscent of the removal of the Central and Embarcadero freeways – in order to facilitate the extension of electrified Caltrain and high-speed rail tracks into the Transbay Terminal.
For almost three years, city planners have been discussing the idea and drawing up closely guarded plans to tear down the freeway, discussions sparked by the state's Environmental Impact Reports on electrifying the Caltrain tracks and bringing high-speed trains into town. With an increasing number of trains traveling those tracks, access to the rapidly growing Mission Bay area from the west on 16th Street would turn into a traffic nightmare, either with long waits for an at-grade train crossing or the creation of ugly and uninviting underpasses for cars and bikes.
Mayor Ed Lee and other top politicians  have long sought to bring those trains downtown in Transbay Terminal through a still-unfunded tunnel , rather than having them stop at the existing Caltrain station at 4th and King streets. But the existence of the I-280 pilings made it structurally impossible to send the train underground before it got to 16th street.
So the idea was raised to raze the elevated 280 freeway and better integrate Mission Bay and the Potrero Hill/Showplace Square area, where Kaiser plans to build a huge new medical facility, creating a bike- and pedestrian-friendly corridor without the shadow of an antiquated freeway overhead.
“If you get the freeway out of the way, it's a ton of space,” said Greg Riessen, the city planner who developed and studied the idea. “The whole corridor of the freeway is blocking the ability to do anything else.”
But it wasn't until the political class and their capitalist partners also realized the enormous development potential of the idea – raising money that could be used to fund the train tunnel – that it was finally floated as a public trial balloon for the first time this week. The Chron's Matier & Ross led their Sunday column  with a short item on the idea, apparently tipped off to its quiet debut a couple weeks earlier.
The city's Transportation Policy Director Gillian Gillett unveiled the idea in a Jan. 7 letter to the Municipal Transportation Commission, repeating it Jan. 10 at a forum on high-speed rail  held at the San Francisco Planning and Urban Research Association. The letter was a response to the MTC's request for information on “San Francisco's policy goals and objectives regarding the much-needed electrification of Caltrain.”
Yet rather than deal directly with that issue, the letter said the answer “must be broadened to address the need for growth in the downtown and South of Market areas,” which it said requires funding to bring the trains into Transbay Terminal and to then let developers have at the 21 acres of land surrounding the existing Caltrain station, where transportation officials planned to store the trains.
“We need to create a faster and cheaper DTX [Downtown Extension project] alignment, realize the full value of the 4th & King Streets Railyard site, and eliminate the intrusiveness of I-280 in Mission Bay by terminating it at 16th Street and replacing it with a boulevard, based on the lessons learned from the removal of the Embarcadero Freeway to create a new Rincon Hill neighborhood, and the Central Freeway to create the new Market-Octavia neighborhood. Reenvisioning Caltrain electrification and the DTX could increase ridership, reduce costs considerably and create additional real estate value that would, in turn, provide for both more jobs to create revenue for both Caltrain and DTX and attract investment,” Gillett wrote.
She calls current plans to electrify Caltrain “shortsighted because it reduces the City's ability to meet its regional job growth allocations, because more than 20 acres are covered with trains, and it eliminates an important opportunity to create real estate value which can be used to fund transit and Caltrain investments,” she wrote.
The letter doesn't address where the increasing number of trains coming into San Francisco would be stored if the railyard is turned into luxury condos and commercial spaces, which has long been a goal of SPUR and other pro-development  cheerleaders. High-speed rail officials have suggested Brisbane, but sources say city officials there have balked at the idea. Although Gillett hasn't returned our calls with follow-up questions, the Mayor's Office seems to see such logistical questions as secondary to this cash-cow idea.
So a staff-level proposal to solve a transportation challenge with an elegant multi-modal solution that follows in the city's tradition of tearing down freeways has morphed into a real estate deal. Quentin Kopp, the father of high-speed rail in California, has already derided the Transbay Terminal project (which is funded by the sale of state land surrounding the site to office tower developers) as little more than a real estate deal, and now the city is apparently seeking to extend that deal further into Mission Bay.
Former Mayor Art Agnos, who worked on both the Embarcadero and Central freeway tear-downs, told us, “In general, I really support the concept of demolishing freeways that bisect the city.”
Yet he said there are many key details and questions that need to be addressed, particularly given the Mayor's Office support for the new Warriors arena  on the Central Waterfront, a project whose unaddressed traffic impacts would be exacerbated by an intensification of development at the Caltrain station, into Mission Bay, and further south.
“It could drown the city, this tsunami of cars, particularly with all the development planned all the way down to Hunters Point,” Agnos said. “I like the idea, but we need a serious discussion of the details, particularly with all these development proposals.”