An investigation was under way to work out why the driver, who has been with the company for three months, took the route, said Red Bus chief executive Paul McNoe.
"Clearly in this case he's decided to take a new route without being aware of the circumstances. It's not a route we'd contemplate sending people down.''
Mr McNoe said drivers were instructed about hazards around the city as part of their training, but he could not confirm if the Richardson Tce bridge was specifically pointed out.
The bus had "crawled'' under the bridge, which had minimised injuries suffered by passengers said Mr McNoe.
Resident Amy Stoop said there was a huge noise when the top of the bus hit the bridge a few houses down from her home, and she had heard a neighbour warning the driver about the danger before it hit.
"She told him to slow down because she knew that he wouldn't fit. But he didn't slow down, he just kept going, and the noise was huge.''
When Ms Stoop went outside to see what happened she found glass and plastic all over the road.
"There was a bit of a mess, glass everywhere. Kids were just crying, a bit dazed and confused. I just felt so sorry for the bus driver, but silly guy.''
"He should've stopped and then analysed the bridge before he attempted to go through it, but he just went straight on,'' said Ms Stoop.
She was surprised a bus would try to drive under the bridge, which had caused problems for several other vehicles.
Mr Ryan said police had spoken to the driver, who would be formally interviewed as part of an investigation, but it was too early to say what action may be taken.
