Techniques for the investigation of road traffic noise in regions of restricted flow by the use of digital computer simulation methods

Computer methods of calculating and predicting the noise from road traffic operating in restricted flow conditions are discussed. A method of calculating the noise from road traffic as a function of the manoeuvring parameters by means of a Monte Carlo digital computer simulation model is briefly described. The model is used in deriving correction contours for single streams of traffic which enable free flow L₁₀ levels to be modified to allow for a flow restriction. Flow restrictions of the type encountered at traffic signals, priority intersections and pelican crossings are considered. The contours cover a stretch of road 600 m long and a distance of 60 m from the kerb line and in general show a reduction in L₁₀ level in transferring from the free to the restricted flow situation. A method of applying the contours as a modification of the United Kingdom Department of the Environment prediction method for L₁₀ is proposed and compared with experimental results. Computer simulation models of complete road intersections are discussed. Two types of intersection controls are considered, the traffic signal control and the roundabout. The results of the two types of simulation are compared and the L₁₀ level adjacent to the accelerating traffic streams is generally found to be greater than that adjacent to decelerating streams. Experimental results for both types of intersection are compared with simulation runs in which the observed traffic parameters are used.     

Synchronized traffic flow simulating with cellular automata model

The synchronized flow traffic phase of Kerner’s three-phase traffic theory can be well reproduced by the model proposed by Jiang and Wu [R. Jiang, Q.S. Wu, J. Phys. A: Math. Gen. 36 (2003) 381]. But in the Jiang and Wu model, the rule for brake light-after switching on, the brake light will not set off until the vehicle accelerates-is obviously unrealistic. Thus we improved the model by considering the difference in accelerating and decelerating performance under different driving conditions. The fundamental diagram and spatial-temporal diagrams are analyzed. We confirmed that the new model could reproduce the synchronized flow by two methods, i.e. the traffic flow interruption effect and performing microscopic analysis of time series data. Simulation results show that the decelerating difference is an important factor to reproduce the synchronized flow. We expect that our work could make contributions to understanding the mechanism of the synchronized flow.     

Influence of expanding ring roads on traffic noise in Beijing City

The road network in Beijing is expanding in the form of loop-lines. Following the 2nd and 3rd ring roads, the 4th has been completed and come into operation in 2002. Traffic noise surveying and analysis was performed along four main roads in the Beijing urban area—the 2nd, 3rd and 4th ring roads circling the central downtown area and Chang-An Avenue, a major east-west corridor through the heart of the city. Measured noise data along the 2nd, 3rd and Chang-An Avenue were compared with the data surveyed before the completion of the 4th ring road for determining influence of expanding ring roads on traffic noise pattern in Beijing City. The results indicate that these main roads remain overloaded by traffic flow during daytime, and noise levels due to road traffic along these roads exceeds relavent environmental standards by 5 dBA. Reduced traffic noise level was observed along the northern half of the 2nd and 3rd ring roads, and along the central section of Chang-An Avenue. Increased traffic noise level was observed along the southern half of the 2nd and 3rd ring roads, and along the non-central section of Chang-An Avenue. Expanding ring roads mitigate heavy traffic flow in the central part of Beijing City, but spread high traffic noise outwards at the same time.     

The annual average sound level of road traffic noise estimated from the speed-flow diagram

The speed-flow diagram correlates traffic speed and traffic flow on a road. The presented method enables estimation of the annual average sound level of the road traffic noise when the characteristics of the diagram are available: traffic flow capacity, free traffic speed, and traffic capacity speed (Fig. 1). Bunches of vehicles decrease the traffic speed and traffic noise.     

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.     

A prediction method for road traffic noise generated from arbitrary non-poisson type traffic flow based on an approach equivalent to that for a standard poisson type traffic flow

In order to establish a prediction method for road traffic noise generated from actual traffic flow of an arbitrary non-Poisson type, a new approach equivalent to that for an idealized Poisson type traffic flow is proposed for practical use. This prediction method is able to treat any kind of road traffic noise fluctuation generated from actual non-Poisson type traffic flow, once information has been obtained on the wave form of the level time pattern observed when one vehicle passes directly in front of an observation point. The validity of the proposed prediction method has been experimentally confirmed by applying it to actually observed road traffic noise data.     

双车道多速车辆混合交通流元胞自动机模型的研究

把NaSch模型的刹车概率分开为独立的加速和减速概率，引入转道规则，建立了双车道多速车辆的混合交通流模型.通过计算机数值模拟，得出了不同参数下混合交通的速度和流量与 密度关系的基本图.结果表明，转道概率、混合比例和加减速概率对混合交通都有重要的影 响，慢车的特性对混合交通起着决定性的作用. 关键词： 元胞自动机 混合交通流 NaSch模型     

匝道系统减速车道对高速公路交通流的影响

主要研究匝道系统减速车道对高速公路交通流的影响.在开放边界条件下,以NaSch模型为基础,建立了含减速车道的出口匝道系统双车道元胞自动机交通流模型.通过计算机数值模拟,得出不同参数控制下的密度、速度、流量和车辆产生概率关系图像,并与不设减速车道的匝道系统进行比较. 关键词： 元胞自动机 匝道 减速车道 NaSch模型     

Road traffic noise prediction based on speed-flow diagram

The method enables calculation of the annual average sound level of the road traffic noise, when the characteristics of the speed-flow diagram are available: the average speed of freely cruising vehicles, capacity of the traffic flow, traffic speed at the traffic flow capacity, and the slope of the decreasing traffic speed versus traffic flow. Under any conditions, traffic congestion reduces the annual average sound level. The final conclusion is that strong traffic congestion cannot be ignored in noise prediction.     

Computer simulation model for the prediction of traffic noise levels

This paper describes a computer simulation model capable of predicting the noise levels generated by traffic passing through road intersections controlled by roundabouts where departures from free-flow traffic conditions occur. The model depends for its operation on the acoustical and flow characteristics of single vehicles travelling on a road from which the overall noise generated by traffic streams can be deduced using a sampling/integration technique. Distance effects, ground cover, vehicle type, velocity and headway characteristics, etc. are taken into account in the model and the simplest possible input parameters are used deliberately to facilitate the eventual use of the model by highway and planning authorities. Good agreement has been achieved between measured and predicted L₁₀ values for freely flowing traffic negotiating roundabouts. Further applications of the model involving road intersections controlled by traffic lights and the effect of traffic queues are nearing completion.     

A road traffic noise pattern simulation model that includes distributions of vehicle sound power levels

Annoyance, sleep disturbance and other health effects of road traffic noise exposure may be related to both level and number of noise events caused by traffic, not just to energy equivalent measures of exposure. Dynamic traffic noise prediction models that include instantaneous vehicle noise emissions can be used to estimate either of these measures. However, current state-of-the-art vehicle noise emission models typically consider a single emission law for each vehicle category, whereas measurements show that the variation in noise emission between vehicles within the same category can be considerable. It is essential that the influence of vehicles that are producing significantly more (or less) noise than the average vehicle are taken into account in modeling in order to correctly predict the levels and frequency of occurrence of road traffic noise events, and in particular to calculate indicators that characterize these noise events. Here, an approach for predicting instantaneous sound levels caused by road traffic is presented, which takes into account measured distributions of sound power levels produced by individual vehicles. For the setting of a receiver adjacent to a dual-lane road carrying free flow traffic, the effect of this approach on estimated percentile levels and sound event indicators is investigated.     

The effects of site selected variables on human responses to traffic noise,part I: Type of housing by traffic noise level

The results of the first part of a field study of human response to traffice noise are reported, along with the general methodology of the entire study. The research was carried out by carefully selecting subjects at sites that had the desired values of selected site variables. Human response measurements were obtained from interviewer administered structured questionnaires, and were as spatially and temporally coincident as possible with the noise measurements. Noise measurements were obtained from six days of rapidly sampled recordings. In this first part the effects of traffic noise level and housing type were considered. Although traffic noise level was the major correlate of the intensity of negative responses to traffic noise, traffic noise level by housing type interaction effects were also observed and were attributed to the accuracy of perceiving the vehicle flow rate and day-night noise level differences. Spontaneous responses supported the validity of the elicited responses.     

Presence of many stable nonhomogeneous states in an inertial car-following model

We present a single lane car- following model of traffic flow which is inertial and free of collisions. It demonstrates observed features of traffic flow such as existence of three regimes: free, nonhomogeneous congested (NHC) or synchronized, and homogeneous congested (HC) or jammed flow; bistability of free and NHC flow states in a range of densities, hysteresis in transitions between these states; jumps in the density-flux plane in the NHC regime; gradual spatial transition from synchronized to free flow; long survival time of jams in the HC regime. The model predicts that in the NHC regime there exist many stable states with different wavelengths, and noise can cause transitions between them.     

Honking noise corrections for traffic noise prediction models in heterogeneous traffic conditions like India

In developing countries like India, the nature of the composition of traffic is heterogeneous. A heterogeneous traffic flow consists of vehicles that have different sizes, speeds, vehicle spacing and operating characteristics. As a result of the widely varying speeds, vehicular dimensions, lack of lane disciplines, honking becomes inevitable. In addition, it changes the urban soundscape of developing countries. In heterogeneous traffic conditions, horn events increase noise level (L_den) by 0.5–13 dB(A) as compared to homogenous traffic conditions. Therefore, the traffic prediction models that are used for homogenous traffic conditions are not applicable in heterogeneous traffic conditions. To increase the accuracy of noise prediction models, in depth understanding of heterogeneous traffic noise is required. Understanding the real traffic noise characteristics requires quantification of some of the basic traffic flow characteristics such as speed, flow, Level Of Service (LOS) and density. In a given roadway, the noise level changes with density and LOS on the road. In this paper, a new factor for horn correction is introduced with respect of Level Of Service (LOS). The horn correction values can be incorporated in traffic noise models such as CRTN, FHWA, and RLS 90, while evaluating heterogeneous traffic conditions.     

An Improved Car-Following Model for Multiphase Vehicular Traffic Flow and Numerical Tests

This paper attempts to introduce an improved difference model that modifies a car-following model, which takes the next-nearest-neighbor interaction into account. The hnprovement of this model over the previous one lies in that it performs more realistically in the dynamical motion for small delay time. The traffic behavior of the improved model is investigated with analytic and numerical methods with the finding that the new consideration could further stabilize traffic flow. And some simulation tests verify that the proposed model can demonstrate some complex physical features observed recently in real traffic such as the existence of three phases： free flow, coexisting flow, and jam flow; spontaneous formation of density waves; sudden flow drop in flow-density plane; traffic hysteresis in transition between the free and the coexisting flow. Furthermore, th.e improved model also predicts that the stable state to relative density in the coexisting flow is insusceptible to noise.     

Vortex sound generation due to a flow impedance discontinuity on a flat surface

The sound generated by the unsteady motion of a vortex filament moving over a flat boundary with a sharp flow impedance discontinuity is studied theoretically. Theoretical results show that the vortex filament undergoes significant accelerating or decelerating motions and radiates sound at the instant when it moves across the plane of impedance discontinuity. The accelerations and decelerations of the vortex filament are shown to be the major mechanisms of sound generation. The sound so produced has a large low-frequency content such that the change in the flow impedance affects only the sound generation process but not the subsequent sound propagation to the far field.     

Evaluation and analysis of traffic noise from the main urban roads in Beijing

Traffic noise surveying and analysis was performed along three main roads in the Beijing urban area—the 2nd and 3rd ring roads circling the central downtown area and Chang-An Avenue, a major east—west corridor road through the heart of the city. The results indicate that these main roads are overloaded by traffic flow during daytime and noise levels due to road traffic along these roads are above relevant environmental standards by 5 dBA. The spatial variance of traffic noise was also analyzed, with the results indicating that the spatial differences result primarily from the unbalanced development of Beijing's urban districts.