Van Ness BRT at City Hall, Alternative 5: center-center median option.
With overwhelming approval for the Proposition K 
transportation sales tax in 2003, San Franciscans signaled they
not only wanted to maintain a state of good repair and operational
solvency for their transit system, they were willing to dedicate more
than 25 percent of the tax to expansion, including a network of transit
preferential streets and Bus Rapid Transit (BRT). The first two BRT corridors will be on Geary Boulevard 
and Van Ness Avenue 
, the latter with a target opening date by Muni's centennial at the end of 2012.
The two routes already carry one tenth of Muni's total ridership and proponents of the BRT treatments expect the improvements in reliability and convenience will attract many more riders. Though Van Ness BRT still has significant hurdles to surmount, including environmental review and securing funding, the planned route has seen scant public resistance, unlike the Geary corridor, where business and community interests in the Richmond have made a bunch of noise about the fear of lost parking and construction impacts. Forty-six percent of people living on the two-mile Van Ness corridor don't own cars, though with transit travel times currently double auto travel times, current mode split only shows around 25 percent of those same people using transit (PDF 
The full-feature Van Ness BRT line is proposed to have physically separated bus lanes that run two miles, from Lombard Street to Mission Street, where the 47 and 49 lines will then re-enter mixed traffic and continue their routes. Buses will be low-floor, with doors for entry on both sides in one proposed option, and signals will be prioritized similarly to light rail vehicles on the Townsend-3rd, and riders will buy tickets before boarding to prevent the significant delays associated with queueing and paying onboard. Station stops would be spaced more than double current stop spacing, or an average of 900 feet, and the TA said its Citizens Advisory Committee (CAC) asked for even greater spacing in several locations at its last meeting.
As part of the MTA's Transit Effectiveness Project 
(TEP), the 47 and 49 buses have been targeted for improvements beyond the 2-mile segregated corridor so that buses avoid delays traveling in mixed traffic for the remainder of their routes. TEP project manager Julie Kirschbaum said the 49 is proposed to make limited stops southbound from Mission Street to City College, while the 14 will run limited and local on Mission Street to make up for fewer stops on the 49. Additionally, the agency expects to place pre-pay ticket boxes along the length of the 49 route, lengthen bus stops to allow the 49 and 14 buses to fit two-deep, and implement signal priority measures to prevent further delay.
Of the estimated $120 million needed to complete the project, the TA estimates that one quarter of the cost will be covered by Proposition K funds, while the rest is expected from the Federal Transit Administration's New Starts 
program. Tilly Chang, the TA's deputy director of planning, pointed out that Van Ness BRT was the only New Starts project in the nation to receive a high rating for cost-effectiveness. Neither the MTA nor the TA were concerned the FTA would provide the requested funding when the EIR is certified in 2010.
Because full BRT treatments are innovative to San Francisco, and would be a first statewide, the TA, MTA, and Caltrans have had to rewrite many of the standards and rules for how streets are used and how buses would travel through them (Caltrans BRT PDF 
). Because Van Ness is a state highway, Caltrans had to change the standards for things as simple as the width and height of BRT station platforms and bulbout crosswalks, which under state standards would otherwise be considered a hazard to motor vehicles.
Advocates have voiced concern that the MTA might not support a dedicated bus lane closed to vehicle traffic, preferring instead to tinker with tools that don't work as well, and cite the underwhelming results of bus-signal prioritization experiments on Geary Blvd downtown. MTA communications director Judson True vowed that the agency is fully-committed to the BRT process, including lane separation for the two miles of the corridor, though acknowledged that they were studying all options as part of due diligence.
As the debate on this blog 
indicates, light rail has a cache in the public eye that BRT doesn't, and the TA acknowledged that it is studying the possibility of a long-term light-rail project built over the existing BRT lanes.
The next TA CAC meeting is Tuesday, March 3rd, from 5-7 pm at the TA offices, 100 Van Ness, 26th floor. CAC meetings are open to the public and all interested parties are encouraged to attend.
And thanks to Chinagirl below for the heads up about the Geary BRT CAC meeting this Thursday, February 26 at 6 pm at the TA offices.