Effects of headway distributions on second order properties of traffic noise

The theory of traffic noise as a generalized shot noise process has been developed by several authors. Implicit in that model is the assumption that the distribution of headways is negative exponential in time or space. This assumption is usually satisfied in light traffic (600 cars/h/lane) but is not adequate for moderate or heavy traffic. The effects are considered of more general headway distributions on the variance of the sound pressure level, the autocorrelation function, and the spectral density. For the set of gamma function headway distributions it is shown that for a fixed traffic density increasing the order of the distribution decreases the variance and tends to emphasize higher frequencies in the spectral density.