SEPTA is altering its service significantly in the wake of the discovery over the weekend of structural flaws that forced them to pull one-third of their Regional Rail train cars out of service. 

SEPTA is going to a modified Saturday schedule designed for weather emergencies beginning July 5, they announced Monday.  

During morning and evening rush hours, all SEPTA Regional Rail lines will be adding extra trains to provide rush-hour service, with extra service available on the Market-Frankford and Broad Street lines to help reduce overcrowding.

"We're adding some additional service in the beginning of the day to help people get into the central business district, and at the end of the day heading back out," said SEPTA General Manager for Operations Ron Hopkins at a news conference Monday afternoon.

About 120 Silverliner V trains, representing some 13,000 seats on the Regional Rail, are being taken out of service after SEPTA maintenance personnel discovered cracking in the main suspension systems Friday.

The cracks are believed to be a structural defect as, after inspections, only five cars did not show the cracks, Hopkins said. 

"Within 24 hours, all Silverliner Vs had been taken out of service," SEPTA said Sunday.

Hopkins cautioned Regional Rail passengers to consider alternate modes of transit, such as buses or subways, as Regional Rail trains will likely face intense overcrowding in addition to reduced service outside rush hour. 

To help passengers take advantage of the Broad Street and Market-Frankford lines' service, parking will be offered at Frankford Transportation Center and AT&T station, and a lot at 601 N. Columbus Blvd. by the Spring Garden Market-Frankford station open from 6 a.m. to 8 p.m., Hopkins said.

All the Silverliner V train cars were acquired between 2010 and 2013 from Hyundai Rotem and are still under warranty, according to SEPTA. Hyundai is working with SEPTA help repair the cars. 

Trailpass card holders are being encouraged to hold onto their cards to be turned into a credit in exchange for lost service, which will be announced in the near future, SEPTA said.

It remains unclear how long resolving the entire situation will take.

"It's too early right now to really zero in on a time," Hopkins said. "Our Regional Rail schedules will continue to evolve over the summer as our Silverliner V cars return to service."

Visit SEPTA.org for the latest possible updates about transit schedules.