Most states are using locked-wheel skid trailers to maintain an inventory of skid numbers (SNs) across their highway networks. The locked-wheel skid trailer does not produce the same SN values as the variable-slip and fixed-slip devices. Thus, a need exists to conduct side-by-side tests to compare the measurements from fixed-slip and locked-wheel skid systems. This paper presents results from tests conducted with fixed-slip and locked-wheel friction measurement systems to investigate relationships between the friction numbers obtained from both systems.