CHICAGO (CBS) The CTA isn’t saying much about its investigation into a Saturday bus crash that injured 37 people along Lake Shore Drive, but union leaders believe maintenance problems could be to blame.

Officials with the Amalgamated Transit Union, Local 241, are calling for an independent review of all CTA accidents to make sure buses are in proper working condition.

They say the transit agency needs more qualified union mechanics to do the work on its buses. Right now, union leaders claim, too much of the maintenance work is being done by outside vendors who are not as familiar with the buses. That could be putting riders at risk.

“They’re just getting lucky, and you shouldn’t put luck when it comes to safety and the riding public,” union representative Carlos Acevedo says of the CTA’s track record on accidents.

Acevedo has worked as a CTA bus mechanic for 14 years, and he’s disturbed by the agency’s maintenance of its fleet. When asked if he thought there were some dangerous buses on the roads right now, Acevedo replied, “Absolutely.”

Acevedo says the union obtained documents from the CTA that support the theory. On Aug. 20, there were 100 buses that were still on the road, even though they were over the recommended mileage to repack the front wheel bearing.

“That wheel bearing fails, causing it to go in a particular direction, and that’s a big, heavy bus to try to maneuver when the wheel bearing hasn’t been properly maintained,” Acevedo said.

The union doesn’t want to speculate on what caused Saturday’s crash, but in talking to the bus’s operator, officials feel improper maintenance could be to blame.

“Her account is more in line with the people I talked to today, that something went wrong with that bus,” said Darrel Jefferson, President of ATU Local 241.

Passengers who were on the bus agree.

“It was a mechanical problem because you should have seen the way the bus driver and the other person tried to turn the steering wheel, and it would not turn,” Britni Jones, who was injured in the crash, told CBS 2 over the weekend.

Acevedo says a variety of maintenance issues, including a ruptured steering line, could lead to a scenario like that. He said trouble with the front wheel bearing also could have lead to a crash like Saturday’s.

The CTA says a preliminary review of the surveillance video on the bus did not show anyone trying to help the operator steer it. Transit officials would not say if the operator herself appeared to be having trouble steering the bus.

The CTA would not release the video. The union wants accident investigations to now be conducted by an independent organization to avoid any conflict of interests, but the CTA says their team is skilled, experienced and fair.