SEPTA's Market-Frankford Line Credit: Screenshot via YouTube

SEPTA found cracks on two train cars on its Market-Frankford Line after first spotting one in a structural support beam during routine maintenance this weekend, the transit authority said Sunday — so they’re pulling a third of their cars as a precaution.

“We will be 30-40 cars short of the 144 needed to run regular, weekday peak hour service levels,” per a notice on SEPTA’s website.

This means the Monday morning commute will be rough, with SEPTA already warning commuters of packed platforms. The morning trains will be supplemented with shuttle buses– for those traveling from 69th Street, these will start at the 52nd Street Station and continue through 15th Street. For those heading in from Frankford in the morning, the shuttle buses will begin at Girard Station and stop at 15th Street.

There’s a plan for afternoon shuttles as well.

The problem follows a rough summer for SEPTA, as cracks were found during routine maintenance of the Regional Rail service, a different type of train — and those cracks pulled about a third of that fleet, as well. That caused persistent overcrowding and delays through the summer months.

Chris Krewson is the executive director of LION Publishers, a national nonprofit association that serves local journalism entrepreneurs build sustainable news organizations, and the founding editor of...