LONGITUDINAL VENTILATION MODEL FOR ONE-WAY TRAFFIC TUNNEL IN CONSIDERATION OF TIME HEADWAY DISTRIBUTION
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Time headway is a significant traffic flow parameter that affects the capacity and safety of highways and freeways. Time headways are broadly used in different areas of traffic and transport engineering such as capacity analysis, safety studies, car following and lane changing behavior modeling, and level of service evaluation. In this paper, the time headway distribution is investigated for an urban highway at different traffic flow rates during congestion. To analyze the headway characteristics, the time headways to the preceding and following vehicles are analyzed for heavy vehicles and passenger cars. The trajectory data used in this study was provided for a highway section in California: Berkeley Highway, I-80. Appropriate models of headway distribution are selected for heavy vehicles and passenger cars using Chi-Square test. Using the selected models, headway distributions are predicted for each vehicle type at different traffic flow rates. The results confirm existence of different time headway distributions in vicinity of heavy vehicles and passenger cars which is due to the difference in the behavior of drivers in vicinity of heavy vehicles and passenger cars under congestion.
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A hazard analysis model was built for the first discharge headway of queuing vehicles at the signalized intersections.The calibration method was proposed for the model parameters and the calibration was performed using the traffic data collected from the signalized intersections in Beijing.The distribution of the first discharge headways in the heterogeneous traffic flow was described and the effects of different factors were analyzed quantitatively.The results show the first discharge headway at the signalized intersections in Beijing is much longer than those in other countries and regions.It is obviously affected by the vehicle type,the complexity of the environment at the intersection and the traffic flow behavior.The starting disturbance increases the average first discharge headway from 3.99 s to 5.47 s,the moving disturbance prolongs it from 4.15 s to 6.65 s,both factors reduce the traffic operation efficiency significantly.
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Generally speaking, traffic headway comprises distance headway and time headway, which varies according to velocity and acceleration. Distance headway is a part of the traffic follow model as an expression of the stimulus-response factor. A more responsive driver accelerates and decelerates more frequently in response to the vehicle in front, thereby reducing the capacity of the traffic lane. This study attempts to calculate the distance headway in both the Macro Traffic Model and the Micro Traffic Model, and thus determine a steady state for the distance headway. The research results show that the Macro Traffic Model reaches Steady State at 20-23 seconds and the Micro Traffic Model reaches Steady State at 19-23 seconds. This research can be applied to traffic planning, calculation of crossroad traffic saturation rates, or in traffic simulation applications.
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Discharge headway is the headway between successive vehicles negotiating an intersection during the green time of signal oper- ation. It is an important parameter in signal operations and analysis since estimation of parameters such as saturation flow and capacity of an intersection depend on it. Although there have been several studies on discharge headway in homogeneous traffic conditions, there are only a few studies on discharge headways in heterogeneous traffic. This study examines the factors affecting discharge headway under heterogeneous traffic conditions which is characterized by mixed vehicle composition and lack of lane discipline. A novel method to measure headways in such cases is proposed here. To get individual vehicle headways, each lane is divided into multiple strips. The width of a strip is approximately equal to the width occupied by a motorcycle. The headways of vehicles in each strip are measured separately and used for analysis. Data collection for the study was carried out at signalized intersections in Chennai, India. Data was collected for one approach at all intersections. From the data collected, headways of individual vehicles were measured. Linear mixed effect regression was used to model discharge headway. The effect of vehicle type, lateral position on roadway, and green time on discharge headway were modeled. From the regression analysis, it was found that all these factors had significant impact on discharge headway. The discharge headway model proposed in this study could be used for obtaining saturation flow rates and capacity at signalized intersections under heterogeneous traffic conditions.
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Akcelik's time-dependent speed-flow model based on queuing theory concepts is used to develop alternative versions of the Highway Capacity Manual speed–flow models for basic freeway segments, multilane highways and urban streets. The corresponding travel time–flow models show that higher-quality facilities have lower levels of bunching delays. A version of the speed–flow model that describes in-stream vehicle interactions and resulting queuing in terms of bunching characteristics is introduced. Speed–flow and headway distribution models for uninterrupted streams are integrated using a common traffic delay parameter. A new model of the proportion of bunched vehicles is proposed for the bunched exponential model of headway distribution. The driver response time parameter at capacity flow is discussed. A model for forced flow conditions is developed, and unsaturated and forced flow conditions are contrasted in relation to determining headway distributions.
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Saturation (graph theory)
Degree of saturation
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Taking the re-distribution phenomen of headway induced by frequent weavingbehavior at weaving sections of urban expressway as research object, theintrinsic rule of automobile headway distribution at expressway was investigated. The conclusion that the distribution of headway varies dynamically with traffic flow rate was obtained. Seven typical cities, such as Beijing, Shanghai, Guangzhou, etc.were chosen as traffic survey areas. The headway data were collected from A-type weaving sections of expressway and then analyzed by statistical, fitting, and 2 test methods. The results indicate that, headway complies with negative exponential distribution when traffic flow rate is no more than 250 veh/h; while flow rate changes from 250veh/h to 750 veh/h, it obeys the displaced negative exponential distribution; however, if the flow rate varies from 750 veh/h to 1 500 veh/h, CowanM3 distribution fits the headway very well. This investigation provides auseful basis for further research on capacity of expressway weaving sections, expressway planning and management.
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This paper looks into the use of the traffic micro-simulation method to assist the tunnel ventilation system capacity design, challenging the traditional traffic assumption of uniform speed and traffic density within a tunnel where grades, on and off-ramps are often introduced. With the micro-simulation method, the vehicle behaviour in tunnel in terms of natural variability in the traffic flow and shockwave movements under super congestion can be fully analysed. Slow speeds produced in the micro-simulation can match the worst scenarios around 2 kilometres per hour, which are not effectively achieved in traditional ways. This paper starts to discuss the method of PIARC, and then introduces the traffic microsimulation software Paramics. A Paramics traffic micro-simulation model was developed for Cross City Tunnel to assist the tunnel ventilation system design. The comparison of the traffic results between PIARC and Paramics is made. (a) For the covering entry of this conference, please see ITRD abstract no. E213716.
Simulation software
Traffic simulation
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