Sampling errors in the measurement of traffic noise with gamma headway distributions

Fisk has elucidated the theory of sampling errors for measurements of noise from traffic characterized as point sources travelling with identically distributed negative exponential headways. The effect of gamma distributed headways is considered here and it is shown that the sampling errors due to the change are small in comparison to the uncertainty built into Fisk's original calculation. The effect of excess attenuation is then considered and it is shown that it can be considerable for parameter values typical of absorption by greenery.