EMBED >More News Videos An Amtrak spokesperson provided an update on the situation at Union Station Thursday afternoon.

CHICAGO (WLS) -- The computer glitch that led to major delays on Metra and Amtrak at Union Station Thursday was caused by a worker falling on a circuit board, Senator Dick Durbin said after speaking with the Amtrak CEO.Senator Durbin said the Amtrak CEO told him Amtrak decided to do a server upgrade during peak hours of service and then a worker trying to repair the problem fell and hit a circuit board.Amtrak released a statement Friday saying the problems were the result of "human error."The statement said,In a statement, Senator Durbin said,Senators Dick Durbin and Tammy Duckworth sent a letter to Amtrak CEO and President Richard Anderson calling for swift policy and operational changes to prevent future equipment failures. The senators also called for the full results of the agency's investigation into the system failure to be made public. Amtrak said it would respond to the letter "in a timely manner."In a statement Friday, Metra said:Metra and Amtrak were operating with normal service Friday, a day after major signal problems brought travel to a standstill for 12 hours at Chicago Union Station.Railroad tracks turned into a parking lot for dozens of trains, some with passengers stuck onboard for hours.The problems started at 8:30 a.m. Thursday. There was a communication issue between Amtrak's computer system and the signal switches at Union Station that halted all train movement, affecting both Amtrak and Metra.It was a domino effect and commuters were stranded for hours while crews worked to fix the glitch."In my time, which is now which his now about 18 years...I've not seen a signal and control system of this duration," said Amtrak spokesman Marc Magliari.Metra warned commuters there would be extensive delays, but no one expected the problems to last over 12 hours.Bibiana Bol is from Kansas City and was heading to a modeling job in Rockford. She had never been on a train before and was still stranded in Chicago Friday morning."I am always known as being punctual so they are going to be shook that I'm not going to be there because this is very important, this is a friend's magazine that I'm supposed to represent and she has a big show coming up so for me, I feel bad because I feel like I let her down," she said.Trains were able to move once again when crews started to manually operate the switches. The system was back in service at around 8:45 p.m.The root of the problem is under investigation, but Amtrak does plan on having additional crews on stand-by Friday just in case.