Commuters in Philadelphia could have some travel troubles come Tuesday.

The city’s transit authority pulled 120 rail cars out of service over what it calls a “significant structural defect.” This comes after workers found cracks in the equalizer beams.

It has caused some significant leaning so far – and the city worries it could get even worse.

Investigators are trying to determine if a design flaw or a manufacturing error are to blame.

While Philadelphia’s commuter rail cars are similar to the ones used by RTD, RTD spokesman Nate Currey says its fleet does not have the same issues.

He says RTD’s rail cars are lighter than the cars in Philadelphia’s fleet and they also use a different platform.

“Ours have a one level platform, they have a high and low level, so that requires some extra equipment,” Currey said. “Ours are about 5,000 pounds lighter than those, so we aren’t expecting to see anything like that.

“We are keeping an eye on things and we’re to be doing every single check that it has, doing a thorough check with that in mind.”

Currey says RTD’s cars undergo maintenance checks about every three weeks.