Speed expert says PM's motorcade well over limit

A Prime Ministerial motorcade between Waimate, South Canterbury, and Christchurch last year travelled an average 44km/h faster than a vehicle keeping to the speed limit, an engineering expert says.

Professor John Raine, a professor of mechanical engineering at Massey University, told the Timaru District Court that tests completed on the same route and keeping close to the speed limits had found an average speed on the journey of about 84km/h.

The motorcade made the same journey at a speed of about 128km/h, Prof Raine said.

A theoretical journey, using computer models based on the speed limits, showed there would be an average speed on the journey of about 90km/h.

Five policemen and a civilian driver are on trial on driving charges arising from the motorcade on July 17 last year.

It is alleged the motorcade travelled at speeds up to 172km/h to reach Christchurch Airport in time for Prime Minister Helen Clark to catch a flight to Wellington for a Bledisloe Cup rugby test match.

Prof Raine said a police Ford Explorer which led the motorcade from Washdyke, near Timaru, to Templeton, near Christchurch, was prone to keeling over and rolling on corners at high speeds.

The case before Judge John Strettell is expected to conclude this week.