A transportation expert says that Monday’s accident involving a Chicago Transit Authority train at O’Hare International Airport could have caused multiple deaths and injuries if it had happened later in the day.

The train was driven by a sleepy operator who investigators suspect fell asleep at the controls.  The train crashed through a barrier, over a platform and then rocketed up an escalator before coming to a stop.

DePaul University professor Joseph Schwieterman said that it was “a miracle that nobody died.”

“A train running up a (crowded) escalator could have been a worst case scenario,” Schwieterman told Fox News. “When pedestrians are hit by a train, it is usual fatal.”

He also said that while many of the passengers suffered injuries, they were lucky that the train jumped the tracks instead of crashing into a concrete barrier at the end of the platform.

“That was a lucky break,” he said. “A train hitting a wall at … high speed could easily have been fatal for many.”

The National Transportation Safety Board is investigating.