A fundamental study of a dynamic modulus for asphalt pavements was conducted using experimental tests and numerical simulations. The emphasis was on the loading frequency-vehicle speed relationships directly caused by the test results of vertical compressive stress pulse durations along the depth. A framework for determining the dynamic modulus is proposed based on the dynamic effects. It is shown that the proposed dynamic modulus is capable of predicting the asphalt pavement behaviour with varying vehicle speeds. The converting factor that can estimate the in situ dynamic modulus from the undamaged dynamic modulus is also proposed using a falling weight deflectometer modulus. Through comparisons with case histories, the maximum relative error of longitudinal strain is 50.4% with an undamaged dynamic modulus and 10.5% with an in situ dynamic modulus. The proposed methods with a converting factor are in agreement with the general trend observed by in situ measurements along the vehicle speeds. © 2013 Taylor & Francis Group, LLC.