The San Francisco Municipal Railway, the busiest public transit system in the Bay Area, is looking to overhaul its routes for the first time in more than 20 years.

City officials have launched the Transit Effectiveness Project, the bureaucratic name for a top-to-bottom review of the system that will map out ways to improve service, attract more riders and increase efficiency.

Any changes are sure to spark public protest because some stops may be removed and some streets may lose parking or a lane for car traffic to make room for bus-only corridors. But in the long run the idea is to make Muni more reliable and to get people to their destinations faster -- once the political hurdles are cleared.

The review, which isn't expected to be completed until the end of next year, comes at a critical time for Muni.

Seven years ago, San Francisco voters passed Proposition E, a reform measure aimed at fixing the troubled transit system that was plagued with breakdowns and long delays. While many improvements have been put in place since -- on-time performance, for example, is much better -- it appears that service is slipping.

"Muni is long overdue for a whole route restructuring," said San Francisco City Controller Ed Harrington, whose office is working on the 18-month study with the Municipal Transportation Agency, which operates Muni. "Travel patterns have changed over the years, and one of the key things we know is that Muni is slowing down every year."