The evaluation of noise from freely flowing road traffic

Roadside surveys of the noise emitted by freely flowing traffic have been made on sites ranging from motorways to urban roads. Sites were generally unobstructed but a few tests were made in places with buildings adjacent to the roadway. The survey also included measurements on two sites involving road gradients.The results provide an indication of present-day traffic noise conditions against which future comparisons may be made and also show how basic variables such as traffic density, speed and composition, and distance from the roadside affect the observed patterns of noise.Agreement between the experimental data and a theoretical analysis of simplified traffic flow forms the basis of a method for predicting the median sound level produced under any given set of traffic conditions. The reliability of the method, provided that due allowance is made for possible ground attenuation effects, is demonstrated using the results of the survey.Finally by a simple extension of the prediction method it becomes possible to take both noise level and duration factors into account and arrive at a figure for total noise exposure from the same traffic flow data.