Without the red signal, the motorists would have passed under the ill-fated bridge near the CSMT railway station, a global heritage site, when a part of it came crashing at around 7.30 pm.
The bridge connected the bustling Chhatrapati Shivaji Maharaj Terminus railway station with the Azad Maidan Police Station.
An eyewitness, who was waiting at the signal, said, "We all were waiting impatiently at the signal as it was red. Before the signal turned green, the bridge came down along with people on it. Had the signal turned green earlier, the situation would have been worse."
"It is the time when entire Mumbai rushes to CSMT to return home. We also wanted to reach home early, but now I feel relieved that the signal was red. Otherwise, I could have been injured as well," he said.
A taxi driver, who was near the bridge when the tragedy struck, had a providential escape, though his vehicle suffered damage.
Vehicles behind him stopped in time, thereby avoiding a bigger tragedy.
The bridge which connected the area near the Times of India building with the iconic CSMT station was commonly knwon as 'Kasab bridge' after the 26/11 Mumbai attack terrorist passed through it during the terror attacks.
This is the third major foot over bridge tragedy in Mumbai in the past 18 months.
A foot over bridge at the Elphinstone Road railway station crashed on September 29, 2017, killing 29 commuters.
The second occurred on July 3, 2018 when a portion of the foot over bridge crashed on the railway tracks near Andheri station, killed at least one and injuring many more.
After the two previous tragedies, the BMC, the Railways and other agencies had carried out a survey of all new and old railway bridges, flyovers, and foot over bridges, to ascertain any dangers and take preventive measures.
Officials claimed that the bridge that crashed on Thursday was found to be sturdy and only needing a few minor repairs.
(With inputs from agencies)