A computer model to predict traffic noise in urban situations under free flow and traffic light conditions

A computer model is presented for predicting traffic noise indices in built-up situations for free flow traffic conditions and for a flow interrupted by a traffic light. The stream of vehicles is simulated by a given time headway distribution, and a transfer function obtained from a 1 : 100 scale model is used to simulate the specific built-up situation. Different time headway distributions result in only very small discrepancies; even the simple “equally spaced” distribution is adequate for predicting noise indices with high accuracy, unless L₉₀ has to be predicted. In eight built-up situations along a road with freely flowing traffic only minor mutual differences are found when L₁ ? L_eq and L₁₀ ? L_eq are compared, but L₅₀ and L₉₀, and consequently TNI and L_np, show discrepancies of the order of 10 dB(A). If a traffic light is introduced the value of L_eq rises compared with the free flow case, and the values of L₁ and L₁₀ increase, especially at higher traffic intensities, while L₅₀ and L₉₀ decrease. If the noise indices are calculated as a function of the distance along the road to the traffic light increases in L₁, L₁₀ and L_eq are found at about 50 m beyond the traffic light. The principal cause for this increase appears to be the differences between the peak levels of an accelerating car and the sound level at the ultimate speed. More in situ measurements are required to test the accuracy of the model, especially for accelerating vehicles.