A critical review of some traffic noise prediction models

Traffic noise prediction models in the 1950s and 1960s were designed to predict a single vehicle sound pressure level Lp at the roadside. These models were based on constant speed experiments, the predicted levels then being expressed as functions of speed, and with zero acceleration. Later models were not intended to predict single vehicle levels but to predict the equivalent continuous level Leq for traffic over a chosen period. Still later models predicted Leq under interrupted and varying flow conditions. Early models predicted linear levels whereas the later models predicted A-weighted levels. Several more recent models predict one-third octave band spectra. Early models assumed single point sources, some assumed short line sources, later ones double point, and even one with thirty-two point sources; some with different spectra. Six commonly used models and others under development are reviewed. The desiderata for traffic noise prediction models are discussed.