Relationship Between Anti-Lock Tire Mark Length and Speed Change 2007-01-0723

The relationship between pre-braking speed and the length of locked wheel skid marks has been explored in many publications. However, the existing literature does not address the effects of anti-lock braking on pre-braking speed calculations based on the length of tire marks. Anti-lock brake systems reduce the wheel slip and avoid wheel lock (100% slip) to enable a vehicle to achieve high deceleration rates under emergency braking while retaining steering control. Typically, during braking an ABS system will maintain 5-25% slip, and can sometimes leave faint and/or alternating tire marks as opposed to the dark skid marks created by a locked sliding wheel. Instrumented vehicle testing was conducted on a variety of vehicles to quantify the effects of pre-mark braking on overall speed change. From this data, the effective deceleration for the tested road surface was evaluated and compared to existing literature for locked wheel braking. This paper evaluates existing published methods to account for the speed loss prior to observing ABS tire marks based on the estimated deceleration and the length of the tire marks. Additionally, this paper explores sources of inaccuracy with estimating pre-braking speed based upon observed ABS tire mark length.