A CAR carrying five teenagers hit a tree at an estimated 40mph, killing rear seat passengers Tristan Cook and Dominic Arnold.
Cheshire Police collision investigator PC Steve Binns told Chester Crown Court on Monday (December 10) that he estimated the car was travelling at 62mph when it spun out of control.
He said he calculated the collision speed by assessing the damage caused to the car.
After reaching this estimated figure he could use average deceleration rates to calculate how fast the car was travelling when it lost control.
PC Binns, who attended the scene on the night of the crash, said he used his police car to do skid tests that measure the grip of the road surface.
He said: “These showed the road surface was of good frictional quality and had no part to play in the crash.”
He added that on examining the scene he found striated tyre marks leading diagonally on the pavement, showing that the wheels were still spinning but moving sideways.
PC Binns said the marks and the eventual landing place of the car suggested it car had suffered the first phase of oversteer as the rear wheel pulls out of line with the front wheel.
He added that the second phase of oversteer occurs when the driver steers the opposite way to try to regain control.
In this case the car rotated clockwise, so that the front of the car faced the opposite kerb.
He said the car suffered a ‘glancing blow’ with a sign post that was bent in two, then hit the tree, climbed partly up the tree before rolling on to the roof.
Tyre pressure checks showed the front tyres were at the correct pressure for an unladen car, but underinflated for the number of passengers in the car at the time of the crash.
The rear tyres were below the manufacturer’s recommended level.
PC Binns said: “The lower the tyre pressure the more the sidewall of the tyre will be able to flex as the car steers into the bend.
“The front tyre here is as you would expect it to be, but as soon as the load shifts to the rear wheels you get a greater slip angle because five people are in the car and the tyre pressures are at or below the minimum setting.
This means the rear of the car wants to travel at a different angle to the rest of the car, and starts to shift outwards.
“So you can see how critical tyre pressures are with a fully-laden car when negotiating a bend at or about the maximum speed for that bend.”
Cheshire County Council highways records showed that their tests of the road surface indicated it needed some attention.
It was re-dressed in August 2007, where a machine cuts small nicks into the top of the surface.
PC Binns explained this is normally done when the force of traffic has ‘polished’ the surface over time.
Morris Lansom-Jones, vehicle examiner for Cheshire Police, told the court he examined Wood’s VW Polo and there was no evidence of mechanical failure causing loss of control.
The case continues.