If you build it -- and offer free hot chocolate -- they will come.

But they might not get off the train. And the train might break down.The TRAX light-rail mass transit system was overwhelmed in more ways than one Saturday as the Utah Transit Authority celebrated the grand opening of its $312 million, 15-mile line connecting Sandy with downtown Salt Lake City.

An estimated 45,000 to 50,000 people took rides on TRAX Saturday -- twice the minimum number UTA general manager John Inglish was expecting. TRAX opens for regular daily service Monday and is projected to carry 14,000 riders a day.

Thousands of would-be passengers queued up at the Delta Center and the other 15 TRAX stations as early as 8 a.m. to take free rides beginning just before noon. They packed the trains, filling many TRAX cars well beyond their unofficial standing-room-only capacity of 150.

Once the rides began, passengers at both ends of the line in Sandy and Salt Lake City waited more than an hour to hop aboard. And once they were on, they tended to stay.

That made squeezing on board from a station in the middle of the line difficult if not impossible. At 1 p.m., volunteers at the Ballpark Station at 1300 South were telling people to go home and come back later because every train stopping at the station was full. At the Midvale Fort Union station, only about 50 people out of several hundred were able to board the first five trains.

By 1:30 p.m., volunteers at the Delta Center were telling arriving passengers to disembark. But some refused, realizing from the length of the line stretching around the Delta Center they would have to wait forever to board a southbound train for a return trip.

At the southern terminus in Sandy, UTA public transit officers and Sandy police had to board trains and ask passengers to leave so people waiting in line could ride. Those people then had to stand in line, most for more than an hour, before boarding a northbound train.

And then one TRAX train developed a problem with its braking system at the Historic Sandy station. That caused a service delay of about an hour, depending on the location, and left many people along the line wondering why the trains had disappeared. Some people simply left. Those stranded by the disabled train waited an hour or more to catch shuttle buses to their cars.

Paul O'Brien, UTA's director of rail service, said there was a brake failure on one vehicle that in turn "scrambled the computer brains" of the other two cars in the train. The vehicle also developed "flat wheels" and as a result had to be moved to the TRAX maintenance facility in Midvale very slowly.

In the meantime, other TRAX cars were routed around that train, and the southern half of the system functioned essentially as a one-track line.

O'Brien said the two cars with computer troubles were to be fixed Saturday night. He said the car that caused the unusual problem would be back in service Monday. A similar breakdown would "absolutely not" happen on Monday, he promised.

"It was a very unusual problem," he said.

The system was up and running again around 3 p.m. but with only 18 of the 23 TRAX cars in service. By 5 p.m., trains were less crowded and lines shorter but waits still were as long as an hour. The free rides continued until about 9 p.m.

"We are so pleased and so overwhelmed by the response from the public," UTA spokeswoman Coralie Alder said.

The large crowd and the mechanical problems prompted Inglish to decide midway through the day that UTA would offer free rides on TRAX again next Saturday. Trains will follow their regular weekend schedule then. Only TRAX will be free, however. Bus fare still will cost $1.

Mamie Soohoo of Holladay, who waited in line for more than three hours with her husband and 7-year-old son, was among those on the first public ride.

"We wanted to be the first to ride the light rail," Soohoo said. "We wanted to do the whole experience."

Betty Hayes came from Wendover and waited in line to get on that first southbound train.

"It's exciting," she said. "I wish they'd put one all the way to Wendover."

Many of those who boarded TRAX were from locations far from the TRAX line, like Holladay, Kearns and Utah County. Some said they came out Saturday because they won't get a chance to ride TRAX on a regular basis. Others wanted to map out what will soon become their regular commuting route.

"For me it's going to eliminate the headache and the crazy drivers on the freeway," said John Brackett, a carpenter who commutes daily from Lehi to work on the Little America expansion project. "If it takes an extra 15 minutes and I can save my sanity, I'll be happy."

LaCosta Hopoate, who has cerebral palsy, was delighted to be the first disabled person to board a TRAX train at the Delta Center.

"I wanted to be first because I wanted to let disabled people know about this," she said. "A lot of disabled people are not sure about this system."

It worked well for Hopoate on Saturday. It took no more than a minute to board, the access ramp was easy for her wheelchair to manage and the TRAX operator was very helpful, she said.

Some people liked Saturday's ride but said they will not use the system often. Cathy Reilly of Holladay said she would have to take two buses with a TRAX ride sandwiched in between to travel to and from her job.

"If I was going to be riding the bus all day, it would make my day way too long," she said.

Bruce Jaynes, an Avenues resident, said he won't be able to use TRAX for work but does plan to take it to Sandy for his cousin's Christmas party this week.

"If they put an east-west line in, I'll use that," he said. "A lot of people will."

The fate of a proposed 2.5-mile extension to the University of Utah's Rice-Eccles Stadium remains in the hands of the Salt Lake City Council. UTA officials and pro-light rail forces within the city were hopeful Saturday's events and this week's start of regular service might sway support.

Salt Lake Mayor-elect Rocky Anderson, among the many dignitaries who boarded TRAX for a brief downtown jaunt to start the day, said he planned to meet City Councilwoman Deeda Seed later Saturday, take her on a TRAX tour and see if that might make a positive impression. Seed is viewed as a potential swing vote among the four council members who voted a month ago to reject the University TRAX extension.

Gov. Mike Leavitt, who helped garner legislative support for west-east funding earlier this year, declined Saturday to enter the debate over University TRAX. It is the only segment of the proposed 10.9-mile west-east line which still could be constructed prior to the 2002 Winter Games.

"There may be a time when I need to make my feelings known," said the governor, who sat near the front of the first train to leave the Delta Center station. "Ultimately I believe east-west rail is a good thing if it can be built in a financially responsible way."

The governor called the ride "smooth and enjoyable" and said he liked the big windows in particular. "It adds a sense of sophistication, I think, to the city."