Capacity at unsignalized two-stage priority intersections

The subject of this paper is the capacity of minor-street traffic movements across major divided four-lane roadways (and other roads with two separate carriageways) at unsignalized intersections. The center of the intersection, corresponding to the width of the median, often provides room for drivers who have crossed the first half of the major road to stop before proceeding across the second major traffic stream. This situation, which is common with multilane major streets, is called two-stage priority. Here the capacity for minor-street through traffic is larger than at intersections without such a central storage space. These wider intersections provide an additional capacity that cannot be evaluated by conventional capacity calculation models. An analytical theory is presented for the estimation of capacity under two-stage priority conditions. It is based on an approach by Harders, although major improvements were necessary to match the results with realistic conditions. In addition to analytical theory, simulations were performed that enable an analysis under more realistic conditions. The result is a set of equations that compute the capacity for a minor-street through-traffic movement in the two-stage priority situation. ©     

The capacity of a priority intersection

We present simple formulae for the maximum capacity of an intersection of a single stream of minor traffic with a single stream of major (priority) traffic. The method allows for both mixed (nonhomogeneous) vehicle types and for inconsistent driver behaviour in the minor traffic stream. For a realistic class of major headway distributions the capacity is the harmonic mean of the capacities for each individual vehicle type. The formulae include generalisations of Tanner's formula for the cases of inconsistent and/or nonhomogeneous minor vehicles.     

城市平面交叉口汽车排放优化策略研究

文章针对城市平面交叉口交通污染严重的问题,分析城市平面交叉口交通及行为特性、影响机动车排放的相关因素,从平面交叉口交通规划、交通控制二个方面阐述汽车排放优化措施。     

A capacity related reliability for transportation networks

A capacity related reliability for transportation networks with random link capacity is introduced. It is defined as the probability that the road network can accommodate a certain level of traffic demand, and is built on the concept of network reserve capacity. Network reserve capacity is defined as the largest multiplier applied to an existing origin-destination demand matrix that can be allocated to a transportation network in a user-optimal way without violating the link capacities. Due to large variability associated with link capacities, a probabilistic approach is adopted to model the different physical and operational factors that often degrade the capacity of roadways. A Monte Carlo simulation procedure is developed to estimate the capacity related reliability measure. Numerical results are provided to demonstrate the feasibility of the approach.     

A multiclass cell transmission model for shared human and autonomous vehicle roads

Autonomous vehicles have the potential to improve link and intersection traffic behavior. Computer reaction times may admit reduced following headways and increase capacity and backwards wave speed. The degree of these improvements will depend on the proportion of autonomous vehicles in the network. To model arbitrary shared road scenarios, we develop a multiclass cell transmission model that admits variations in capacity and backwards wave speed in response to class proportions within each cell. The multiclass cell transmission model is shown to be consistent with the hydrodynamic theory. This paper then develops a car following model incorporating driver reaction time to predict capacity and backwards wave speed for multiclass scenarios. For intersection modeling, we adapt the legacy early method for intelligent traffic management (Bento et al., 2013) to general simulation-based dynamic traffic assignment models. Empirical results on a city network show that intersection controls are a major bottleneck in the model, and that the legacy early method improves over traffic signals when the autonomous vehicle proportion is sufficiently high.     

Limited priority merge at unsignalized intersections

The development of a new gap acceptance model based on limited priority for the major stream is discussed. Field observations were carried out to identify the mechanism of the merging process taking place at unsignalized intersections under congested conditions. It was found that the major stream headways were increased due to the merging vehicles, particularly at high flows. A limited priority system is proposed based on the assumption that the major stream vehicles would be slightly delayed to accommodate the minor stream vehicles. Equations for capacity in the limited priority system are presented assuming the major stream vehicles to have a bunched exponential headway distribution and the minor stream drivers to be both consistent and homogeneous. The gap acceptance model based on the limited priority was then applied to the performance of roundabouts. It was found that the limited priority merge can have a significant effect on the entry capacity at two-lane roundabouts. A near linear relationship between the entry capacity and the circulating stream flow at two-lane roundabouts was identified which was similar to the empirical results from the UK. ©     

Assessment of factors associated with travel time reliability and prediction: an empirical analysis using probabilistic reasoning approach

Significant efforts have been made in modeling a travel time distribution and establishing measures of travel time reliability (TTR). However, the literature on evaluating the factors affecting TTR is not well established. Accordingly, this paper presents an empirical analysis to determine potential factors that are associated with TTR. This study mainly applies the Bayesian Networks model to assess the probabilistic association between road geometry, traffic data, and TTR. The results from this model reveal that land use characteristics, intersection factors, and posted speed limits are directly associated with TTR. Evaluating the strength of the association between TTR and the directly related variables, the log odds ratio analysis indicates that the land use factor has the highest impact (0.83) followed by the intersection factor (0.57). The findings from this study can provide valuable resources to planners and traffic operators in their decision-making to improve TTR with quantitative evidence.     

Maximum car ownership under constraints of road capacity and parking space

This paper presents a model for determining the maximum number of cars by zones in view of the capacity of the road network and the number of parking spaces available. In other words, the proposed model is to examine whether existing road network and parking supply is capable of accommodating future zonal car ownership growth (or the reserve capacity in each zone); i.e. the potential maximum zonal car ownership growth that generates the road traffic within the network capacity and parking space constraints. In the proposed model, the vehicular trip production and attraction are dependent on the car ownership, available parking spaces and the accessibility measures by traffic zones. The model is formulated as a bi-level programming problem. The lower-level problem is an equilibrium trip distribution/assignment problem, while the upper-level problem is to maximize the sum of zonal car ownership by considering travellers’ route and destination choice behaviour and satisfying the network capacity and parking space constraints. A sensitivity analysis based heuristic algorithm is developed to solve the proposed bi-level car ownership problem and is illustrated with a numerical example.     

A new approach to evaluating on-road public transport priority projects: balancing the demand for limited road-space

Despite widespread growth in on-road public transport priority schemes, road management authorities have few tools to evaluate the impacts of these schemes on all road users. This paper describes a methodology developed in Melbourne, Australia to assist the road management authority, VicRoads, evaluate trade-offs in the use of its limited road-space for new bus and tram priority projects. The approach employs traffic micro-simulation modelling to assess road-space re-allocation impacts, travel behaviour modelling to assess changes in travel patterns and a social cost benefit framework to evaluate impacts. The evaluation considers a comprehensive range of impacts including the environmental benefits of improved public transport services. Impacts on public transport reliability improvements are also considered. Although improved bus and tram reliability is a major rationale for traffic priority its use in previous evaluations is rare. The paper critiques previous approaches, describes the proposed method and explores some of the results found in its application. A major finding is that despite a more comprehensive approach to measuring the benefits of bus and tram priority, road-space reallocation is difficult to economically justify in road networks where public transport usage is low and car usage high. Strategies involving the balanced deployment of bus and tram priority measures where the allocation of time and space to PT minimises negative traffic impacts is shown to improve the overall management of road-space. A discussion of the approach is also provided including suggestions for further methodology development.

A note on the interpretation of the dual variables in estimating traffic capacity at signal- controlled road junctions

The values of the dual variables in a constrained optimisation problem can be used to estimate the sensitivity of the optimal value of the objective function to changes in the constraints. Allsop (1972) used standard methods of linear programming to derive expressions for the sensitivity of the reserve capacity at a signal-controlled road junction to various changes in the traffic engineering constraints. That analysis used the assumption that the maximum reserve capacity would be achieved when the cycle time used is maximal. While this normally occurs, some junctions have come to light where a reduction in the cycle time increases the capacity. Allsop's analysis is extended here to account for this possibility.     

Stability of transportation networks under adaptive routing policies

Growing concerns regarding urban congestion, and the recent explosion of mobile devices able to provide real-time information to traffic users have motivated increasing reliance on real-time route guidance for the online management of traffic networks. However, while the theory of traffic equilibria is very well-known, fewer results exist on the stability of such equilibria, especially in the context of adaptive routing policy. In this work, we consider the problem of characterizing the stability properties of traffic equilibria in the context of online adaptive route choice induced by GPS-based decision making. We first extend the recent framework of “Markovian Traffic Equilibria” (MTE), in which users update their route choice at each intersection of the road network based on traffic conditions, to the case of non-equilibrium conditions, while preserving consistency with known existence and uniqueness results on MTE. We then exhibit sufficient conditions on the network topology and the latency functions for those MTEs to be stable in the sense of Lyapunov for a single destination problem. For various more restricted classes of network topologies motivated by the observed properties of travel patterns in the Singapore network, under certain assumptions we prove local exponential stability of the MTE, and derive analytical results on the sensitivity of the characteristic time of convergence to network and traffic parameters. The results proposed in this work are illustrated and validated on synthetic toy problems as well as on the Singapore road network with real demand and traffic data.     

An intersection turning movement estimation procedure based on path flow estimator

Estimation of intersection turning movements is one of the key inputs required for a variety of transportation analysis, including intersection geometric design, signal timing design, traffic impact assessment, and transportation planning. Conventional approaches that use manual techniques for estimation of turning movements are insensitive to congestion. The drawbacks of the manual techniques can be amended by integrating a network traffic model with a computation procedure capable of estimating turning movements from a set of link traffic counts and intersection turning movement counts. This study proposes using the path flow estimator, originally used to estimate path flows (hence origin–destination flows), to derive not only complete link flows, but also turning movements for the whole road network given some counts at selected roads and intersections. Two case studies using actual traffic counts are used to demonstrate the proposed intersection turning movement estimation procedure. Copyright © 2010 John Wiley & Sons, Ltd.     

Simultaneous control of traffic lights and bus departure for priority operation

This article presents a bus priority method for traffic light control based on two modes of operation: immediate and controlled departure. The immediate departure mode is a standard procedure in which the intersection controller grants priority upon request of the bus. Controlled departure acts to avoid a second stop of the bus at the end of the queue formed during red by holding the bus at the bus stop, while still granting priority to the bus lane. Selection of one of the two modes is based on intersection cost that includes bus delay and the impact on the overall traffic near the intersection. The method is applied in a constant cycle scenario where green recall and green extension can only be granted within certain limits. Numerical examples illustrate the application of the approach.     

Traffic signal timing problems with environmental and equity considerations

Traffic signal timings in a road network can not only affect total user travel time and total amount of traffic emissions in the network but also create an inequity problem in terms of the change in travel costs of users traveling between different locations. This paper proposes a multi‐objective bi‐level programming model for design of sustainable and equitable traffic signal timings for a congested signal‐controlled road network. The upper level of the proposed model is a multi‐objective programming problem with an equity constraint that maximizes the reserve capacity of the network and minimizes the total amount of traffic emissions. The lower level is a deterministic network user equilibrium problem that considers the vehicle delays at signalized intersections of the network. To solve the proposed model, an approach for normalizing incommensurable objective functions is presented, and a heuristic solution algorithm that combines a penalty function approach and a simulated annealing method is developed. Two numerical examples are presented to show the effects of reserve capacity improvement and green time proportion on network flow distribution and transportation system performance and the importance of incorporating environmental and equity objectives in the traffic signal timing problems. Copyright © 2013 John Wiley & Sons, Ltd.     

Induced traffic and economic appraisal

Economic appraisal of major roads in the UK is based on a set of standard procedures and conventions. A central assumption has been that the volume and pattern of traffic in any given year is independent of the quality of service offered by the network — the fixed trip matrix assumption. Failing to consider induced traffic can have serious consequences for the accuracy and robustness of the measured traffic benefits from road improvements. Assessment of the wider economic benefits of roads, which is an important political imperative for road investment, is also made more difficult. Two conclusions are reached. Variable trip matrix methods need to be introduced for the appraisal of major road schemes, and scheme appraisal needs to be complemented by a more strategic area-wide approach to evaluation. In responding to its advisory committee (SACTRA), the UK Department of Transport has accepted the first of these conclusions and is cautiously favourable to the second.     

公路养护管理发展探讨

公路的养护管理是延长公路使用寿命,保证交通运行顺畅的重要管理手段。本文主要针对当前公路使用过程中出现的主要病害,结合节能环保的时代主题,针对公路的主要病害分析公路养护过程中主要养护技术的开展,以望为提高公路养护管理水平提供一定的参考价值。     

基于关联规则的重大道路交通事故影响因素分析

相比于一般交通事故,重大道路交通事故的特征及其影响机理会有所差异,本文旨在研究重大道路交通事故的分布特征及其主要影响因素。收集2014至2018年的重大道路交通事故数据,从驾驶员行为、车辆状况、道路线形和时空分布方面对重大道路交通事故的基本特征进行分析,采用关联规则技术深入挖掘重大道路交通事故多因素的影响机理。从人、车、道路和环境四个方面,重点讨论了重大道路交通事故中的两因素和三因素交互作用的影响机理,并据此提出了针对性的事故预防措施。     

A driving force model for non-strict priority crossing behaviors of right-turn drivers

At urban intersections, conflicts between right-turn vehicles and through non-motorized vehicles are a critical cause of traffic congestion and safety challenges. Based on the fact that in different countries there is no strict priority in conflicts between motorized and non-motorized vehicles, this study focused on analysis of the inherent mechanism of this universal phenomenon. By the analogy of a force model for moving vehicles, this paper developed a micro driving force model, including the safety driving force and efficiency driving force, for right-turn drivers which constitute the dominant party during the non-strict priority crossing process. We further demonstrate that the strict priority crossing behavior is a special case of the proposed driving force model. All the parameters used in this model were calibrated through field data collected at twelve signalized intersection sites in Shanghai. Model validation results proved the accuracy and reliability of the proposed driving force model. The model was further proved that it can be used for right-turn vehicle's average crossing speed prediction. The sensitivity analysis identified the influence of vehicle type, non-motorized traffic flow rate, and non-motorized traffic speed on the average speed, and offered support for the rationality of the non-strict priority.     

Managing Traffic by Privatization of Road Capacity: A Property Rights Approach

Abstract

Road congestion remains a serious problem, despite all the efforts to limit road use and to manage growing road traffic volumes. Economic approaches (such as pricing) are introduced based on traditional welfare economic theory. Although they are sometimes very successful, the magnitude of traffic issues also requires alternative and unconventional approaches. Perhaps a more innovative perspective is needed. The paper discusses an alternative economic approach starting from property rights theory. It is translated in transport systems in concepts of infrastructure capacity slot management, where slots are dynamically priced and exclusively allocated to individual users. Debates and practices regarding this approach in air traffic and rail traffic are further developed than in the field of road traffic. The paper aims to explore the potential benefits and disadvantages of the property rights approach for road traffic. Attention is paid to major institutional and technical conditions. The conclusion is that the approach theoretically has clear advantages and seems technologically feasible. Nevertheless, serious political and institutional issues have to be solved first.     

Crash analysis at intersections in the CBD: A survival analysis model

Enhancing the safety level of urban roads especially in CBDs is paramount. Due to a large number of intersections in what is usually a grid road system in the CBDs, we investigate crashes occurring in and around an intersection. The question of interest in this study is: does the nature of crashes at intersections differ from those of the roads at midblock? Stated more precisely, considering the intersection as a reference point, does the distance to the reference point (i.e. midblock locations on the roads) correlate with different types of crashes compared to that of the intersection? A right answer can lead traffic engineers and safety auditors to propose different safety measures at intersections and the midblock locations. As a pilot study, we collected the last 9 years crash data of the CBD of Melbourne, Australia. For the first time, we employ Survival Analysis models -including Exponential, Weibull, and Log-logistic- to investigate a space-dependent phenomenon (i.e. accidents at proximity to the intersection). Of the outcome, highlights are: (i) police presence at busy intersections during busy night outs and weekends highly improves the pedestrian safety (ii) raised crossings at midblock locations lower likelihood of crashes of pedestrians as well as cars, (iii) lighting conditions at intersections must be watched and kept at a high level. (iv) Severity, likelihood, and location have no known association with the level of congestion. In other words, safety is first, always and everywhere. The results can be of interest to traffic authorities and policy makers in reinforcing traffic calming measures in the cities. The codes developed in this study are made available to the research community to be used in further studies.