The Central Scotland Police Volvo, driven by Pc Jacob Marshall, clipped a car on the M9.
The incident happened as off-duty taxi driver Fraser Lenny, 49, who was returning from a fishing trip in a Vauxhall Zafira with an 80-year-old passenger, pulled out to allow other traffic from the M876 to merge onto the M9 from a slip road.
Falkirk Sheriff Court was shown a video of the incident filmed by a camera mounted on the police car’s dashboard which showed the Volvo was travelling at high speed before it hit the car.
Barry Manson, a constable who was a passenger in the Volvo, told the court that the police car was travelling at speed to deal with an incident on the M80 involving spilled diesel. He said the diesel was “like black ice” that could have led to a “serious road collision”.
He added: “On a daily basis, police are travelling at speeds of 150 miles an hour on the M9.”
Mr Lenny said the incident occurred around 9:30am on August 29, 2010.
He said he had checked his mirrors and indicated before pulling into the outside lane to let drivers in from the slip road.
He said: “I did not hear any siren. I just saw blue flashing lights at the last minute, then a bang, and my mirror was off.”
He said he followed the police car, which pulled over. A police officer got out and asked if Mr Lenny and his passenger were alright, he told the court. An officer called an ambulance to the scene as Mr Lenny was so shocked. He said: “I was shaking like a leaf.”
Mr Lenny’s 80-year-old passenger, Archie Lane, said the impact had caused “a terrific bang”.
Pc Manson, 30, said he and Pc Marshall had been at Stirling when they got the call to attend the diesel spill on the M80.
He said he had seen “no indication” that Mr Lenny was going to pull into the outside lane.
Sgt Graham Adamson, 42, who investigated the accident, said the call to the diesel spill was a “grade one” call – the most serious kind.
He told the court: “Drivers are permitted to drive above the speed limit for these grade of calls.
“Out of built-up areas they are permitted to drive to up to 95 per cent of the capability of their car, which can be up to 150 miles per hour. But they are not required to drive at this speed.”
Pc Marshall, 31, of Stirling, denies dangerous driving. The case, before Sheriff William Gallacher, will continue on 10 February.