It's a crack so significant that sources tell ABC7 the only things keeping the front and back of the bus together were power steering and cooling lines, plus that rubberized material that gives the bus it's accordion look.
The bus was not carrying passengers at the time. And others like it won't be for at least a few days.
More than 200 CTA buses - out of service and under the spotlight - are idle on Thursday night, spilling out of garages across the city.
"People could get hurt under those circumstances," said Darrell Jefferson, Amalgamate Transit Union.
The CTA's employee union provided ABC7 with pictures that they say shows the breaking point. It's called a hubler joint, a critical component that attaches the front of the bus to the rear. It cracked on Wednesday on a bus that was only five years old.
"That's a very dangerous thing to happen. The front of the bus could keep going and the rear would be wherever it wanted," said Jefferson.
The CTA is moving quickly, pulling 226 buses manufactured by North American Bus Industries off the road. That represents roughly 6 percent of the CTA's bus fleet.
"We have to replace them with smaller buses so there is an impact in terms of amount of people who can ride the buses during this period," said Dorval Carter, acting CTA president.
It isn't the first problem to pop up with this brand of bus. In 2005, the CTA stopped payment to the same manufacturer after signs surfaced that brand new buses were prematurely wearing. At the time, small cracks were also noted.
"Once the inspections are done and if it's determined by our experts that the buses are safe then we will return them to service," said Carter.
The CTA operates according-style buses from several manufacturers so you may still see some on the streets.
On Thursday night, ABC7 found no evidence that the bus safety alert has gone national to include other transit agencies.
A spokesperson for the bus manufacturer did not return ABC7's calls or email for comment.
For more information on CTA routes affected by this alert, please visit http://www.transitchicago.com/travel_information/alert_detail.aspx?AlertId=902