The influence of towing speed on the effectiveness of the 4-sided impact roller using earth pressure cells (EPCs) is investigated. Two field trials were undertaken;the first trial used three EPCs placed at varying depths between 0.5 m and 1.5 m with towing speeds of 9-12 km/h. The second used three EPCs placed at a uniform depth of 0.8 m, with towing speeds of 5-15 km/h. The findings from the two trials confirmed that towing speed influences the pressure imparted to the ground and hence compactive effort. This paper proposes that the energy imparted to the ground is best described in terms of work done, which is the sum of the change in both potential and kinetic energies. Current practice of using either kinetic energy or gravitational potential energy should be avoided as neither can accurately quantify rolling dynamic compaction (RDC) when towing speed is varied.