CHICAGO (CBS) — Human error. That’s what caused Thursday’s nightmare of delays for more than 60,000 passengers at Union Station. CBS 2 has learned a worker fell on a circuit board during a server upgrade.

CBS 2’s Megan Hickey is always investigating and has the story from Union Station with Amtrak’s stunning admission.

The biggest question: Why did Amtrak decide to do a server upgrade in the middle of rush hour? Amtrak is apologizing but local lawmakers said it’s not enough.

On Thursday, Union Station was packed with stranded passengers all day. Trains moving out slowly, one at a time, because all of the signals had to be switched manually. That’s when Amtrak said it didn’t know the source of the computer failure.

But on Friday, CBS 2 learned that the network crash around 8:30 a.m. Thursday was due to a worker falling on a circuit board during a server upgrade.

“It makes no sense to be doing any kind of work changes during rush hours,” said U.S. Representative Dan Lipinski.

He is the chairman of congressional subcommittee that oversees railroads. He met with Amtrak’s CEO last month about the need for work on the rails and crumbling concrete inside Union Station. He said now he’ll be meeting with him again next week about Thursday’s operational failures.

“Metra passengers deserve much better than what they’ve been getting,” Lipinski said.

Senators Dick Durbin and Tammy Duckworth are also pushing for answers. They said in a statement in part:

“We urge Amtrak to immediately address the causes of yesterday’s system failure and to implement policies and operational changes necessary to prevent this from happening again.”

Amtrak declined requests for on-camera interview, sending a statement that again apologized to Metra and to everyone who was impacted.

Meanwhile, a railroad operations and safety expert said he has never heard of a malfunction like this in his decades of experience and questioned why it took so long to fix the outage.

“To knock that much down and not have that kind of back up. I haven’t heard of one this big happening before,” said Richard Beall.

In a statement Metra said they expect Amtrak to take immediate action to prevent this from happening again.