Talk of San Francisco’s next freeway removal has heated up since a proposal from the Mayor’s Office to take down the northern spur of I-280 went public. The highway teardown would open up land for housing, connect neighborhoods, and help bring high-speed rail and Caltrain downtown.

“The good news is this would be the third segment of freeway we will have removed,” said Livable City Director Tom Radulovich, referring to the removal of the Central and Embarcadero Freeways, which revitalized the neighborhoods the roads used to divide. “Before each of those freeway removals, carmageddon was predicted, and it didn’t happen.”

While San Francisco officials say they’ll have to go though years of analysis and negotiations before any decision is made, building public support will take some work, judging by the outraged listeners who chimed in on the issue on an edition of KQED Forum last week.

On the forum, SF Planning Department Director John Rahaim stopped short of endorsing the proposal, but acknowledged, “If it works from a transportation standpoint, we think there could be some substantial benefits: increased park space, reconnecting Mission Bay to the rest of the city, opening up land for development, and connecting that part of that city that is kind of divided right now by the freeway.”

Transportation agencies certainly seem to be thinking seriously about the highway removal. Ben Caldwell, a masters student at UC Berkeley’s Department of Urban Design, did recent a project [PDF] analyzing the removal of the same same section of freeway (completely coincidental to the mayor’s proposal), and he’s already been invited to make presentations for staff at the SF Municipal Transportation Agency and Caltrans. (He hasn’t presented it to them yet.)

When researching Caltrans data on how much car traffic 280 carries, Caldwell said the numbers varied depending on the source, but that the freeway’s capacity was underused. That bolsters the case that turning the skyway into a boulevard wouldn’t result in major car congestion. “It seemed to me that Caltrans was being a little cagey about admitting what the data was, because the traffic volumes on that section of 280 are extremely low — far too low for a freeway of that capacity,” said Caldwell. Caltrans hasn’t responded to a request for comment.

Contrary to the popular misconception that elevated roads are needed to carry a fixed amount of car trips, a lot of freeway traffic evaporates when the highway is removed. As Radulovich explained, past freeway removals (as well as freeway expansions) have shown that highways actually generate a certain level of demand for driving that is reduced once they’re gone, especially as transit, walking, and biking alternatives are improved. As the area around Mission Bay grows, maintaining the freeway will only encourage commuters to drive.

“The amount of traffic on city streets is, to some degree, a function of how easy you make it to get there, and how much automobile capacity you provide,” said Radulovich. “Providing more automobile capacity often gets you more vehicle trips, removing it often gets you fewer.”

Traffic patterns also change as drivers take different routes. As Rahaim noted on KQED, one advantage to removing the 280 highway into a street-level boulevard would be that “you can disperse traffic more quickly from 16th Street, so it’s not all going to those two ramps that exist today.”

It’s not hard to imagine what a surface-level boulevard version of 280 would look like: King Street, the surface-level extension of 280, shows the contrast between a street integrated into the neighborhood and a blight-inducing, neighborhood-severing elevated highway structure.

A look at the planned network of unbuilt freeways in San Francisco can also help explain why elevated structures aren’t necessary. If mid-century city planners had gotten their way, and the freeway revolt failed to sway the Board of Supervisors to vote reject the freeway plans, highways would today overshadow neighborhoods from the Haight-Ashbury (with no Panhandle) to the Marina to the Mission. If we lived in that alternate universe, would proposals to remove those highways be met with similar predictions of carmageddon?

Tim Colen, director of the Housing Action Coalition, said the organization is “very excited” about the 280 proposal, which would allow the development of neighborhoods that were displaced or never built because of the structure. With the real estate tax revenue it would generate to help fund high-speed rail, it’s a one-time opportunity. “The principle seems straightforward and easily supportable,” said Colen. “Use the enormous value of the land beneath and adjoining the I-280 freeway to underwrite getting high-speed trains buried and all the way to the Transbay Center.”