What is a Skid Test Unit?
Affectionately called a “Skid Truck,” it consists of a tow vehicle – a one-ton crew cab pickup pulling a specially designed two-wheel trailer. this combination conforms to ASTM E-274’s “Constant Velocity, Locked Wheel, Skid Testing Unit” specifications. What does it do? The vehicle travels down the road to be tested at a constant steady velocity which is almost always 40 MPH. At the appropriate time the system is activated and the automatic skid cycle commences. Water is pumped out in front of the trailer test tire. In ODOT’s case, this is the left tire. A very powerful braking system locks this wheel. Sensitivive instruments measure the horizontal and vertical forces acting on this tire. These numbers are averaged over the test interval and produce a “Skid Number.” View video of Skid Test Unit: Drive Along View Drive By View What the heck is a “Skid Number?” A skid number is basically the average coefficient of friction across the test interval. It is calculated by dividing the horizo
