To study the dynamic interaction between flexible pavement layersa special equipment was designed and built and a testing methodologywas also developed. Theoretical analysis and initial testing havedemonstrated qualitative aspects of the phenomenon. On such basisit was suggested to represent the horizontal interaction betweenflexible pavement layers as a structural restraint following Kelvin'smodel. The representing parameter has been defined by the authorsas: Interlayer Reaction Complex Modulus Kl*. The statistical characteristicsof the test developed were evaluated, together with the valuesof the norm (absolute value) and of the phase angle (between loadand deformation) of the vector KI* at two different temperatures.Statistical analysis has shown that test reliability is adequatefor research purposes but still low for normalization. The testand the parameter KI* appear to be suitable for the representationand evaluation of the interaction between asphalt concrete layersfor flexible pavements.