Electromagnetic (EM) wave absorbers have been used for improving the EM environment of an electronic toll collection (ETC) system on an express highway or a wireless local area network (LAN) system in an indoor environment. In this paper, an efficient multi-ray propagation model, which uses 3D geometry and image techniques to trace multiple signal rays from transmitter to receiver, is employed to analyze the EM environment of a dedicated short-range communication (DSRC) system on an express highway. The validity of the model employed is discussed by the comparison with the results obtained by an experiment on the highways. The analysis shows that the possible undesired communications between onboard equipment that acts as a receiver and DSRC beacon which transmits the radio signals, is improved by increasing the EM wave-absorption capability of the sidewalls and the pavement of the highway. Another advantage of the employed model is that it is effective for investigating the location of wave absorbers to be set up on the highway, and it takes only a fraction of a minute for computation.