Driver Braking Performance as a Function of Pedal-Force and Pedal-Displacement Levels

Driver-vehicle tests were performed in which the deceleration/pedal-force ratio (i.e., gain), pedal-displacement level, speed, surface-tire friction, and driver characteristics were systematically varied in order to determine the influence of these variables upon minimum stopping distance and other performance variables.

Tests performed on a low coefficent of friction surface showed that high values of deceleration/pedal-force gain result in a greater number of wheel lockups and longer stopping distances compared to results achieved with intermediate or low deceleration/pedal-force gains. Tests performed on the two test surfaces with high and intermediate levels of friction showed that low deceleration/pedal-force gains produced longer stopping distances than were obtained with high gain, even though a high-gain brake system causes higher frequencies of wheel lockup. There were no significant differences in braking performance attributable to pedal-displacement level except that a zero-displacement pedal resulted in a significantly larger number of wheel lockups.

The findings are discussed and evaluated with respect to developing recommendations for standards on pedal-force levels and deceleration/pedal-force gains. The data show that drivers are unable to utilize all of the braking capability existing in the test vehicle when it is necessary to modulate the pedal force to maintain steering control and path stability.