The T line has never lived up to its promise. Coming...

Jamil Wardlow leaves his Bayview home an hour early whenever he has to catch the T-Third Street Muni Metro. The line runs so late, and the trains are so sluggish, that he needs that extra time, he said.

Lamar Reed said he once got so tired of waiting for the T that he walked five miles to get downtown from Kirkwood and Third streets.

These aren’t outlier stories; they are typical rider experiences on a troubled light rail line that has never lived up to its promise of delivering brisk, convenient transit service to one of the city’s most isolated and least accessible pockets. Too often, riders say, the line is either stuck at one of the many intersections along its route or idling in car traffic.

Muni aims to deliver T trains within eight or nine minutes of each other during commute hours, but records show it’s falling short of that goal. Throughout the week of Sept. 15, trains arrived in the desired intervals about 65 percent of the time. The following week, they hit their target 64 percent of the time, and they inched up to a 67 percent success rate the week of Sept. 29.

“The idea was a fast, frequent, fairly high-capacity transit line to serve the eastern waterfront neighborhoods, which are the fastest-growing neighborhoods in the city,” said Tom Radulovich, executive director of the nonprofit group Livable City.

“But,” he added, “that isn’t what we built.”

The line is about to enter its next phase, when the Central Subway opens in 2019. At that point, the San Francisco Municipal Transportation Agency will reroute the T near Fourth and King streets, piping trains into a tunnel beneath Fourth Street, where they will zip north under South of Market to a new station in Chinatown.

“Once they open the Central Subway the whole rail line will improve,” said former SFMTA board chair Tom Nolan. He hopes that by 2020, trains will skate from Visitacion Valley and the Bayview up to Stockton Street.

The T line’s problems appear to stem from its design. It hits about 60 intersections looping from Sunnydale to the Folsom portal, where it travels underground to Embarcadero Station and then changes signs to become the K-Ingleside. Most of those intersections have traffic signals that don’t always sync up to give trains priority over other vehicles.

T trains also get stopped by cars making illegal left-hand turns. And while trains use dedicated rail lanes along the norther portion of the route, in the Bayview, they shift to mixed traffic roadways, which are usually jammed with cars and trucks.

Then there’s the drama of the Fourth and King Street intersection, near the Caltrain depot and AT&T Park. Riders seem to collectively hold their breath as the T heaves to a stop — maybe for one minute, maybe five.

Several riders who spoke with The Chronicle feared that the new Central Subway project will only bifurcate the T route, producing snappy trips between Mission Bay and Chinatown but disregarding the more impoverished neighborhoods in the Bayview, Visitacion Valley and Sunnydale.

“At 23rd Street — that’s about where the gentrification stops,” said longtime rider Mico Williams, referring to a street about midway through the Dogpatch neighborhood. It’s an area of craft breweries and spruced-up Victorian homes, just north of the more working-class Bayview community.

T riders like Katy Birnbaum, the programs and development director at Livable City, see the 23rd Street rail stop as a symbolic border that cuts off the Bayview from the rest of the city. It’s close to Muni’s Islais Creek bus and train yard, so in the evenings many T trains go out of service at 23rd Street, leaving passengers stranded. Birnbaum said she sometimes walks the last mile and a half to her home near Kirkwood and Third streets.

“If you haven’t passed 23rd Street by 7 p.m., you’re out of luck,” she said. “You might wait an hour for the next train that goes to the end of the line.”

San Francisco’s southeast quadrant has long been a transit desert, said former District 10 Supervisor Sophie Maxwell, who represented Bayview-Hunters Point, Dogpatch, Visitacion Valley and Portrero Hill. MTA officials addressed residents’ desperation for better service when they presented the T rail concept in the 1990s, saying it would provide a swifter, smoother ride than Muni’s 15-Third Street bus. Eventually, it would connect a growing Asian American community in Visitacion Valley with downtown and Chinatown, an aim of the late Chinatown power broker Rose Pak, who became the Central Subway’s biggest champion.

“We had high hopes that it was really going to help our neighborhood,” said longtime Visitacion Valley resident Fran Martin, who participated in several community advisory groups to help plan the T. “Oftentimes, being at the edge of the city, you just don’t get any attention.”

But when the first trains began rolling along the $667 million railway in 2007, complaints came almost immediately. The 5.1-mile line was burdened by delays — particularly in the Market Street Subway tunnel — and residents pined for the bus it had replaced.

“All those projections about it saving 10 minutes to get downtown, I don’t think people bought it,” Maxwell said. “And that’s certainly not how it played out.”

Her successor, Supervisor Malia Cohen, inherited the T’s beleaguered riders upon taking office in 2011.

“The complaints I heard from people seven years ago are the same I hear today,” said Cohen, who has pressed the MTA to launch an express commuter shuttle that would complement the T route.

In the meantime, MTA officials are making investments to improve the T, starting with new software to sync up traffic signals and allow trains to glide through intersections. The agency will tackle the bottleneck at Fourth and King streets first, said Muni director John Haley, and then fix the rest of the Third Street corridor. Plans are also inching along for a loop at 25th and Illinois streets, so that T trains can shuttle between Dogpatch and downtown at peak commute hours, ferrying more commuters along the most popular stretch of the route.

This year, the agency doubled the size of many T trains from one to two cars to alleviate overcrowding.

All of these efforts combined “will provide much better, more frequent service,” said Haley, who tells a story of once counting cans in a Safeway window display while waiting for the T to move. “Soon you’ll be going too fast to count cans.”

At the same time, development has accelerated in eastern waterfront enclaves like Dogpatch, Mission Bay and Potrero Hill. A new hospital opened on Fourth Street, and the Warriors’ 18,000-seat Chase Center arena is scheduled to open when basketball season begins next year.

Skeptics say the T line improvements that Muni is making won’t accommodate the surging population and needs in these areas. Trains can only run about 200 feet long — the length of a block in the Bayview — which means they can carry only two of Muni’s German light-rail cars.

“When you think about the growth and development planned in the eastern portion of the city, it’s a lot more demand for transit than we are building transit capacity for,” Radulovich said.

Even so, politicians and transit officials still champion the T as a great social equalizer, saying it could pump business into the city’s most neglected neighborhoods and give those residents a quick link to the downtown core. In the future they hope to extend the subway line further north to Fisherman’s Wharf.

That whole interconnected vision won’t work unless Muni fixes the line’s problems south of Fourth and King streets, said SFMTA board chair Cheryl Brinkman.

Now might be the time to make improvements, Brinkman noted, with Mayor London Breed pressuring the MTA to upgrade Muni service, the new Warriors arena opening and Cohen serving as president of the Board of Supervisors.

“There is no physical or engineering reason why we can’t speed up transit,” Brinkman said. “But it takes political will.”

Rachel Swan is a San Francisco Chronicle staff writer. Email: rswan@sfchronicle.com

Twitter: @rachelswan