The Downtown Rail Extension or DTX is the final, very expensive piece in the construction puzzle that will make the new Transbay Transit Center more than just really fancy bus station. But as we've been hearing for several years now, the Transbay Joint Powers Authority (TJPA) still doesn't know how they'll be paying for it, and construction budget overruns on the Transit Center have further complicated that. Now, as Socketsite reports following a recent presentation to Caltrain's board of directors, we'll be looking at a really fancy bus station for at least the next decade — with underground rail construction not getting completed from the existing Caltrain depot at Third and King to the new Transit Center until 2026 at the earliest.

Bus service to and from the Transbay Transit Center is set to begin by late 2017, and some long ago estimate had Caltrain service coming to the transit, via a 1.3-miled underground tunnel to be built beneath Second Street, by 2018 (see animated rendering above).

As of early last year, it sounded like at least some of the funding for the DTX had been secured via a Mello-Roos tax district that developers in the Transbay District all ultimately agreed to after some hemming and hawing.

As of a couple years back, this is what the SF County Transportation Authority was saying on the funding issue:

TJPA is exploring the feasibility of alternative project delivery options, including Public Private Partnership (P3) as means to reduce cost and accelerate delivery. Transportation Authority staff will continue to work closely with TJPA, the City, and other funding partners to support delivery of Phase 1 and to advance strategies to close the funding gap for Phase 2.

Now the TJPA will be working on a funding plan over the next year, set to be complete by mid-2017, in order to cover the cost of the DTX, now estimate at $2.6 billion.

AND the drama surrounding the sinking of Millennium Tower, which sits next door to the Transit Center, has caused some early funding for the DTX already to get delayed. As the Chronicle reported in September, the Board of Supervisors, in their role as the San Francisco County Transportation Authority Commission, voted unanimously to delay $6.8 million for phase two of the Transit Center project, which includes the DTX and pedestrian tunnels connecting the center to BART and Muni. The reason for the delay being that the City wants to make sure that the TJPA won't be on the hook for the Millennium Tower's troubles, which the sinking and tilting tower's developers have publicly said they should be.

After bailing out the Transit Center to the tune of a $260 million loan last year, the City is now fully in bed with the TJPA and wants to make sure that they won't come calling for even more money down the line.

The final piece of the Transbay Transit Center will of course be the completion of the high-speed rail from Los Angeles, which will be sharing electrified tracks with Caltrain up the Peninsula and also use the DTX to ferry passengers into SF. And we will all be lucky to see that thing running during our golden years.

All previous Transbay Transit Center coverage on SFist.