A Ballarat bus driver who injured six people when he crashed his coach into the notorious Montague Street bridge in South Melbourne has been jailed for five years and three months.

Key points: The judge said it was astonishing Aston did not see the bridge

He said the driver, not his employer, was ultimately responsible for the crash which injured six

The driver will serve a minimum of two-and-a-half years in prison

Jack Aston, 55, was driving for Gold Bus Ballarat on February 22, 2016, when the front of the bus struck the base of the bridge, which had a three-metre clearance.

His vehicle was 3.8 metres high.

In October, a jury found Aston guilty of six charges of negligently causing serious injury.

The court heard there was a sticker on the driver's instrument panel indicating the height of the bus.

"Three of your passengers saw the bridge. How it is that you did not, is astonishing," Judge Bill Stuart told Aston during sentencing.

"Why you were so grossly inattentive is unknown to me.

"Driving an 11-tonne bus with 14 passengers and failing to observe any of the warnings … is itself in my view a serious example of this offending."

Six passengers were injured in the crash. ( Twitter: Metropolitan Fire Brigade )

Judge Stuart noted that Gold Bus founder Donald McKenzie had taken responsibility for not warning Aston of driving conditions in that area.

Mr McKenzie told a plea hearing in the County Court last week Aston had been "let down by the company".

"I'd like to apologise on behalf of the company to the six passengers who were injured.

"I'd also like to apologise to Jack and his family who have been put through the mill," Mr McKenzie said.

But the judge said Aston was ultimately responsible.

"Employers cannot be blamed for [the] obvious failings of employees."

The plea hearing last week was told Aston, an experienced driver, was "confused" and had failed to see numerous warning signs over a 300 metre stretch of road.

But the judge rejected these assertions from his defence team.

"I don't know how you could possibly have been confused," Judge Stuart said.

The judge pointed out that one of the warning signs along the route was a height sensor which triggered red flashing warning lights.

Aston had dropped off passengers at the Melbourne Convention and Exhibition Centre and was taking others to a hotel on St Kilda Road when the crash occurred.

VicRoads installed an overhead height warning system at the bridge after the incident. ( ABC News: Danielle Bonica )

The court heard it took 48 seconds for Aston to drive less than 300 metres from a traffic intersection on Munro Street to the bridge.

The bus was travelling at 56 kilometres per hour at the time of impact.

At the plea hearing, Aston's lawyer, Richard Edney, spoke of the "history of a bridge that is so damning and so extensive" that meant there were "lurking dangers" for drivers in that area.

"It is a bridge built in the 19th century trying to do work in the commercial, industrial world of the 21st century."

Mr Edney was also critical of the road design.

A few months after the accident, VicRoads installed rubber flaps on an overhead gantry to warn drivers of the bridge's low clearance.

Judge Stuart ruled Aston would serve a non-parole period of two-and-a-half years.