Before the doors to the Expo Line train slid open, letting in a gust of hot summer air, Metro riders at the Farmdale station in West Adams had already backed away from the edge of the platform, shaking their heads.
The train, packed with evening commuters, pulled away without anyone boarding.
"I love the train, but I don't think I can keep doing this," said Cindy Rodriguez, 38, who had stood in the sun for half an hour as two full trains passed by. "At least you can get on the bus."
Two months after the debut of light-rail service to Santa Monica, it has become clear that the Metropolitan Transportation Authority does not have enough rail cars to accommodate the Expo Line's surging ridership.
A years-long series of delays in acquiring cars for several new rail lines has left Metro without a way to meet demand. If officials could lengthen trains with additional cars, "we wouldn't be having the same conversation," chief operations officer Jim Gallagher said.
Seasoned riders and transit newcomers have griped about cars so jammed during peak hours that there is no room for bicycles, wheelchairs or, at some stations, any more passengers. Packed cars are expected from time to time, they say, but a 12-minute wait for the next train exacerbates the problem.
Weekday trips on the Expo Line have jumped by half since trains began running to Santa Monica, eclipsing the performance of other Metro routes during their first months in operation — a robust but not entirely surprising outcome for a line that helps traffic-weary Westsiders avoid congestion.
In June, the 11.5-mile Expo Line saw nearly as many trips as the Gold Line, which is twice as long.
"It's a good thing, to have lots of riders," Gallagher said. But, he added, "if we'd had another 10 cars or so a couple months ago, that would have been great."
The crunch began in 2008, when Los Angeles County voters approved a half-cent sales tax increase to fund the construction of nearly 30 miles of light rail and the acquisition of hundreds of new rail cars.
Metro officials considered buying an extra 100 vehicles from an Italian company that was already building 50 for the system. But the first cars from AnsaldoBreda arrived years late and nearly three tons overweight.
By the time Metro signed a $900-million contract with Osaka-based Kinkisharyo International in 2012 for 235 new vehicles, the agency's chief executive warned that "the past two years have used up what slack we had."
Kinkisharyo delivered the first sleek, silver-and-yellow car with a speed that impressed Metro officials. Still, staff members noted, it took Kinkisharyo several months to work up to the agreed-upon delivery rate of one vehicle per week.
"That's not unusual in a car series," Gallagher said. "They may be a little bit late, but they have production pretty well settled."
Tests on the new cars have also taken longer than planned. Metro has received 41 vehicles from Kinkisharyo, and is still testing 13, a few of which "aren't behaving properly," Gallagher said.
The Expo Line runs two- and three-car trains that arrive every 12 minutes during the day and every 20 minutes after 8 p.m.
By December, Metro should have received and tested enough of the Kinkisharyo vehicles to run two-car trains every six minutes, officials said.
The length of the platforms typically prevents Metro from running trains longer than three cars. But agency officials have said in contract documents that they aim to run three-car trains every six minutes by next year or the year after.
More immediately, crowding on the Expo Line should gradually ease this year as more cars are put into service, officials say. In the meantime, riders should adjust to very full cars.
"We're not Amtrak and we're not an airline," officials said in a blog post earlier this year. "We want a train that carries more people than just the number of seats."
Riders should try to remain polite in close quarters, and anyone with a bicycle should stay in the marked bike area or wait for the next train, spokeswoman Pauletta Tonilas said.
Frustrated riders say trains so crowded that they cannot board is not uncommon, particularly at stations that are in the middle of the line. Others worry that a few particularly ugly commutes on the Expo Line could influence how often new transit riders will take the line in the future.
Jessica Pace, 31, takes the train from North Hollywood to a nonprofit in West Adams three days per week. Trains headed to downtown Los Angeles are often so full, she said, that her office will often let the co-workers who are in the biggest hurry board the train first, and everyone else will wait.
"I hate L.A. traffic, but I've really contemplated buying a new car," Pace said. "Sitting in traffic has to be easier than the overcrowding."
Other riders have complained about smaller issues that Metro expects will be worked out in coming months, including how confusing service delays can be to new riders. Real-time screens sometimes show the wrong station information, or the wrong arrival times.
Erik Weber, 30, lives in Highland Park and takes the Expo Line to a venture capital firm in Santa Monica. He prefers taking the train to driving, he said, but noted that Metro could work on better communication with its customers about delays and service changes.
"It's like watching a teenager go through growth spurts," Weber said. "I don't expect perfection, but I want this thing to be better, because I love it."