San Francisco’s Municipal Railway may have a hard time running on time, but at least the transit agency is doing more to let riders know when their next bus or streetcar is due to arrive.

The "NextMuni" system, which tracks the location of vehicles via satellite, is now up and running on all the city’s electrified trolley bus lines. It had been available only on the Metro streetcar lines and the 22-Fillmore, a trolley bus line that served as an early test.

The whereabouts of the Global Positioning System-equipped vehicles are fed into a centralized computer system that translates the data into user-friendly updates available on the Internet and on cell phones and personal digital assistants.

Muni also plans to display the arrival times on electronic information boards posted in bus shelters. The message-board hookups — already operating in some shelters — should be completed by the end of April, Muni spokeswoman Maggie Lynch said Wednesday.

Eventually, Muni’s fleet of diesel buses and the famed cable cars will be added to the program.

Greg Dewar, who posts the N Judah Chronicles blog, is already sold. "I use it all the time,'’ he said. He has the program on his cell phone, including a special link for the N-Judah stop at Irving Street and Ninth Avenue.

"It’s not perfect, but it gives you a better sense of when the train will get there — or not get there," he said. "And then you can decide what you want to do."

The NextMuni updates tell people when the next bus or streetcar is supposed to arrive at a particular transit stop — for example, a 5-Fulton will arrive at Fulton Street and Masonic Avenue in 4 minutes, followed by another in 16 minutes and another in 29 minutes.

There’s a caveat: An unexpected traffic jam, an unruly passenger, or a mechanical problem on the bus could delay the actual arrival time. The system, however, is supposed to provide real-time adjustments.

In another effort to make Muni more user-friendly, the city will sell monthly FastPasses on the Internet, starting April 10.

Meanwhile, drivers will be able to go online and purchase prepaid parking cards, which can be used at all parking meters in the city except those operated by the Port of San Francisco located along the Embarcadero and along some streets in Fisherman’s Wharf. The cards will be available on the Internet starting April 2.

Updates on Municipal Railway lines

– NextMuni is available on all the Municipal Railway Metro streetcar lines and this month was expanded to all the trolley bus lines: the 1-California, 3-Jackson, 4-Sutter, 5-Fulton, 6-Parnassus, 7-Haight, 14-Mission, 21-Hayes, 22-Fillmore, 24-Divisadero, 30-Stockton, 31-Balboa, 33-Stanyan, 41-Union, 45-Union/Stockton and 49-Van Ness/Mission.

For more information, go to www.nextmuni.com.

Buy FastPasses, parking cards online

– Starting April 10, the city will sell monthly Muni FastPasses on the Internet at www.sfmta.com. FastPasses can be purchased from the 10th through the 22nd of each month for the next month. The first shipping date for orders containing FastPasses is the 19th of the preceding month.

The city also will start selling on the Internet at www.sfmta.com. prepaid parking cards for use at city parking meters. Sales will start April 2.