The accidents have marred what was to be a moment of rejuvenation for the city. The opening of the rail line was timed to coincide with a major spruce-up of downtown, complete with a fountain that flanks the tracks and sends water leaping high into the air each time a train approaches.

So far, 15 motorists have driven into the fountain.

None of the train-versus-car accidents have been fatal, and more than half have simply been fender benders, according to the Metropolitan Transit Authority's statistics.

Still, experts say that while it is hard to compare light rail lines - each has its own length and configuration - Houston's accident rate is extraordinarily high. Sacramento, by comparison, where that part of the light rail line that shares the street is about the same length as Houston's line, has had just four collisions this year.

The situation has quickly become part of Houston lore. At an annual sand castle competition this month, no fewer than 11 entries depicted trains and crashed cars, with titles like "Metrozilla" and "Weapons of Mass Destruction."

And residents are keeping score.

"I was No. 6,'' said Joseph D. Kittrell, a 64-year-old hairdresser who suffered a couple of broken ribs and whose Nissan truck was totaled when he turned left over the tracks while a train was coming. Mr. Kittrell, given a ticket for an illegal turn, said the signage was confusing.

"I wrote the mayor, I wrote The Houston Chronicle," he said. "I feel like I've been had by the city, and I don't think it's fair."

The train, which opened for business on Jan. 1, carries passengers from the new Reliant Park football stadium north through the Texas Medical Center complex, the museum district and downtown, where it cruises down the center of Main Street, past the baseball stadium, to the University of Houston's downtown campus. It is intended to be the spine of a much larger system to come, which voters approved by referendum in early November.

That was before they knew what it would be like to share their streets with a 99,000-pound train that travels at 40 miles an hour and is separated from cars only by little bumps known as traffic buttons. Many people now question the wisdom of the transit agency's decision to wedge the train into the streetscape instead of above or below ground, an option that could have increased costs tenfold.

Officials of the transit agency, known as Metro, do not come right out and say so, but their explanations for the accidents boil down to this: Houstonians are bad drivers. All the collisions, they say, can be attributed to driver error: illegal turns, failure to yield and disregard of signals.

There is plenty of support for that argument. The accident rate in greater Houston, train or no train, is well over double the national average, and it is particularly bad at the medical center. Last year the police issued 8,000 traffic citations along what has become the train's route.

"Unfortunately we lead the state in every conceivable type of crash," said Ned Levine, the transportation program coordinator for the Houston-Galveston Area Council, the region's planning group .

Thirty-nine percent of serious accidents here are caused by speeding, compared with 13 percent nationally, Dr. Levine said, adding, "I would call that aggressive driving.''

But the transportation agency's efforts to defend itself have not gone over well. "It's not just the media," said Frank J. Wilson, who became chief executive of Metro two months ago. "It's the general perception, people in the street, elected officials. They say: 'What's wrong with Metro? Why is it blaming these motorists?' As if it's a God-given right in Houston to run red lights."

It did not help matters that the first driver to collide with the train was a local television reporter.

To be fair to Houston drivers, they have had to master six new and complex traffic signs, including an icon that shows a train track, over which is superimposed a left-turn arrow, over which is a circle with a slash through it. The signs are symbols only, without words like "warning."

At the medical center, the train's path doubles as a left-turn lane. At other points, driveways exit right onto the tracks. In Mr. Kittrell's case, the traffic lights were green, but centered above them was a new signal forbidding a left turn.

"I said, 'Well, who's going to look up there when there's two green lights?' " he recalls telling the police.

Metro has since moved no-turn signals to make them more visible.

Some drivers complain that the train comes without the typical warnings.

"Are you from America?" Benny Delgadillo Sr. said indignantly. "I'm from America, 49 years. Here, you're taught as a kid that flashing lights, arms come down - train's coming."

Mr. Delgadillo admits, however, that he should not have turned left where he did, off Main Street. He made a common mistake: he and the train in the lane to his left were traveling in the same direction, so he did not see it when he made the turn.

"It's just even by the grace of God that I should be talking to you now, it hit me that hard," he said.

Metro has made numerous adjustments: changing and moving signs, adding flashing lights and more flashing lights. In February, it commissioned the Texas Transportation Institute, at Texas A&M University, to do an independent study. The study concluded that the route met national traffic standards, but suggested 161 "enhancements," many involving signals and their timing.

Since the agency began adopting those changes, the rate of accidents has been declining, and transit experts say it will continue to drop as Houston and the train grow accustomed to each other.

For now, safety engineers have determined that trains and cars are too hostile to even share an intersection. In the most accident-prone part of the route, red lights halt cars from all directions when a train is passing through, a signal pattern called "pre-emptive red."

Though Metro strongly disagrees, some drivers point to the improvements as evidence that the city was at first negligent.

Maria Lewis-Sterling, a 46-year-old nurse, says her car was not even moving when its license plate was torn off by a passing train. Her car was protruding into the roadway, though, and she was charged $450 for damage to the train. Her accident was the first of six at one intersection, which has since been given two rail crossing signs.

Ms. Lewis-Sterling said she had no hard feelings, and even rode the train to work this week. "Just give me my $450 back,'' she said, "and admit that you didn't do a perfect job.''

Metro's ridership is averaging 24,000 on weekdays and continues to increase. Now, in part because of continuing concern over the accidents, its board has asked the agency to re-examine the planned routes for the light rail expansion.

But besides cost considerations, Metro officials say, there are other reasons to build a train on street grade. It is more accessible and easier to use, and it fosters what Houston lacks: street-level development and pedestrian culture.

"I'm trying to decide what the balance is: safety versus accessibility, ease of mobility versus changing culture," said Mr. Wilson, Metro's chief. "Some people would say, 'If you do it again, would you do it the same way?' My guess is that after a lot of deliberation and hammering, we probably would."