Sandy Murray, of Police Scotland’s road policing unit, was giving evidence at the trial of bus driver Callum Phillips, who denies killing 39-year-old Ryan Baird by dangerous driving.
Phillips, 49, from Dalbeattie, Dumfries, is alleged to have caused the Nith Valley Rangers supporters bus to crash at the Crossroads Roundabout, near Kilmarnock, on October 1, 2016.
Mr Baird, from Sanquhar, Dumfriesshire, who was trapped in the wreckage, died. He and 36 fellow Rangers fans were travelling to Glasgow for a home match against Partick Thistle.
Constable Murray, who was a police collision investigator from 2007 until 2017, told the High Court in Glasgow that he examined the tachograph on the bus which showed how fast it was being driven.
He said a one point the bus was travelling at 73mph – 23 mph higher that the speed limit for buses on the A76 which is 50mph.
The jury was told that as the bus travelled from Thornhill, Dumfries-shire towards Kilmarnock, picking up Rangers fan en route, it was frequently well above the 50mph limit.
It was reported as travelling in excess of 62mph between noon and 12.03pm, between 12.20pm and 12.45pm and between 12.53pm and 1pm.
Mr Murray said: “At 12.24pm it reached a maximum speed of 73mph.”
The police officer said that in his opinion Phillips had applied the brakes as he approached the roundabout and this caused the near offside wheels to lock approximately 50 metres from the roundabout junction.
He said that tyre marks found on the road demonstrated that the brakes were working.
Mr Murray added: “Mr Baird was standing in the aisle at the rear of the bus. He was found under the nearside of the bus, having been partially ejected via a broken window.
“The collision was the result of Callum Phillips driving the bus in excess of the speed that was safe to negotiate Crossroads Roundabout.
“He was regularly driving in excess of the maximum speed limit and the wheel marks on the road show that he braked successfully..”
The police officer added: “This collision was the result of Callum Phillips driving at speed which was inappropriate for the road layout.”
The trial before judge Lady Stacey continues.