Heavy Truck Safety Performance Measures

Braking efficiency - the fraction of the available tire-road friction that can be used without locking any wheels

Braking stability - a measure of the directional stability of a vehicle under combined braking and turning

Dynamic load-transfer ratio - the fractional change in load between left and right side tires in an evasive maneuver

Effective overhang ratio - the distance from the turn center to the rear of the trailer divided by the trailer wheelbase

Friction demand - the tire-pavement friction necessary for a truck to turn without jackknifing

Friction utilization - the ratio of braking force to vertical load at each axle

High-speed steady state offtracking - the lateral offset between the path of the first axle and the path of the last axle in a steady turn

High-speed transient offtracking - the lateral overshoot of the last axle with respect to the path of the first axle in an evasive maneuver

Low-speed transient offtracking - the lateral offset between the path of the first axle and the path of the last axle in a right angle turn

Rearward amplification - the ratio of the highest lateral acceleration of the last trailer to the highest lateral acceleration of the tractor during evasive maneuver (primarily of concern for multi-trailer units)

Static rollover threshold - the lateral acceleration at which the truck rolls over in a steady turn

Understeer coefficient - a measure of how aggressively a truck responds to a steering input at a given lateral acceleration

Yaw damping ratio - a measure of the attenuation in trailer oscillation initiated by a steering input