Vehicular Flow Research Articles

Vehicular Ad Hoc Networks

With vehicular ad hoc networks gaining an ever-increasing interest to serve a diverse variety of applications in today’s intelligent transportation systems, it was not at all surprising for the guest editorial team to receive a handful of submissions for this special issue addressing different aspects and test-beds of vehicular networks. In sum, 8 papers were accepted to be published in the special issue. An interesting note to make is that 5 of the accepted papers had an actual experimental implementation carried out in the road and under real-world conditions. This certainly helps to justify their application and usefulness for future deployment by the industry and authorities.While all papers address enhancing the safety and efficiency of driving, each of them addresses a certain aspect of this issue. The paper by M. J. Flores et al., “Driver Drowsiness Warning System Using Visual Information for Both Diurnal and Nocturnal Illumination Conditions,” seeks to locate, track, and analyze both the drivers face and eyes to compute a drowsiness index under varying light conditions (diurnal and nocturnal). In their paper “Multiobjective Reinforcement Learning for Traffic Signal Control Using Vehicular Ad Hoc Network,” D. Houli et al. propose a new multiobjective control algorithm based on reinforcement learning for urban traffic signal control, named, multi-RL. M. Tsukada et al. in “Design and Experimental Evaluation of a Vehicular Network Based on NEMO and MANET,” present a policy-based solution to distribute traffic among multiple paths to improve the overall performance of a vehicular network. The paper “Traffic Data Collection for Floating Car Data Enhancement in V2I Networks” by D. F. Llorca et al. presents a complete vision-based vehicle detection system for floating car data (FCD) enhancement in the context of vehicular ad hoc networks. S. Miyata et al. in “Improvement of Adaptive Cruise Control Performance” propose a more accurate method for detecting the preceding vehicle by radar while cornering. The paper “Reducing Congestion in Obstructed Highways with Traffic Data Dissemination Using Ad hoc Vehicular Networks” by T. D. Hewer et al. presents a message-dissemination procedure that uses vehicular wireless protocols to influence vehicular flow, reducing congestion in road networks. M. Koubek et al., in “Reliable Delay ConstrainedMultihop Broadcasting in VANETs,” focus onmechanisms that improve the reliability of broadcasting protocols, where the emphasis is on satisfying the delay requirements for safety applications. Finally, M. G. Cinsdikici and K. Memis in “Traffic Flow Condition Classification for Short Sections Using Single Microwave Sensor” seek to identify the current traffic condition by examining the traffic measurement parameters and taking into account occupancy as another important parameter of classification. We hope this special issue can help the research community further its understanding of this emerging field.

Comparative study of levels of care in children exposed to environmental noise on three campuses in the city of Guadalajara, 2009.

Noise is a pollutant that significantly affects the quality of life and health of individuals. Individuals exposed to noise may experience stress, discomfort, sleep disturbances, impaired immune system, lack of alertness, hearing loss (to varying degrees), cardiovascular disease, increased aggressiveness of individuals, low productivity, and traffic and workplace accidents. [WHO (1999); Berglund and Lindvall (1995); Clark et al. (2006); Haines et al. (2001)]. In the city of Guadalajara, a large number of schools are located on heavy traffic roads or busy streets, or in hot spots of environmental noise caused by motor vehicles, which exposes children and teachers who attend them to unfavorable acoustic conditions to develop their school tasks. Thus having a negative effect on their attention span, memory, and performance, as well as damaging physical and emotional health. This study aims to contribute to the study of sound quality by means of the analysis of noise conditions at elementary schools, which were located at critical points in terms of heavy vehicular flow. Besides, it analyzes the perception of environmental noise within the same facilities, and how this compares with results from schools located in quiet streets.

Reducing Congestion in Obstructed Highways with Traffic Data Dissemination Using Ad hoc Vehicular Networks

Vehicle-to-vehicle communications can be used effectively for intelligent transport systems (ITSs) and location-aware services. The ability to disseminate information in an ad hoc fashion allows pertinent information to propagate faster through a network. In the realm of ITS, the ability to spread warning information faster and further is of great advantage to receivers. In this paper we propose and present a message-dissemination procedure that uses vehicular wireless protocols to influence vehicular flow, reducing congestion in road networks. The computational experiments we present show how a car-following model and lanechange algorithm can be adapted to react to the reception of information. This model also illustrates the advantages of coupling together with vehicular flow modelling tools and network simulation tools.

From traffic breakdown to energy flow analysis

Usually a traffic breakdown is defined as a speed drop of a certain amount within a dense traffic situation. To describe these dynamics successfully a probabilistic model is chosen where the unpredictable influences are summarized by a stochastic force creating vehicular platoons out of the metastable free flow. In this way the speed drop mentioned above is translated into an overshot of the threshold given by the critical cluster size. The vehicular flow as an open nonequilibrium system of driven or active particles has energy sources like gasoline and energy sinks like road friction. Here we investigate the flux of mechanical energy to evaluate the energy balance out of the given nonlinear dynamical system of vehicular particles. The long-time result, either fixed point or limit cycle depending on traffic density, is characterized by a certain energy value. In order to understand the traffic breakdown as transition from free flow to congested traffic we estimate the total energy per car at low and high densities and observe the energy of jam formation. This picture of energy consumption cannot be prompted by field observations directly. Nevertheless the idea of an energy picture in traffic is quite attractive and pathbreaking.

The New Steel-and-Light “Doorway” for the City of Padova

The City of Padova is an important trading hub in the north-eastern industrious region of Italy, located near the intersection of the major highways crossing the country in east-west and north-south directions. The ring of speedways that distribute the vehicular flow inside the city was completed by a new viaduct, near the gate of A4 toll road. Its particular location and its relevant functional and architectural values make it the most important access to the city, and this was the expectation of the Public Administration of Padova. The Corso Argentina steel viaduct is 544 m long and 13,5 m wide. It has 11 spans in bending continuity and two separate ways are borne by V-shaped piers that are also in bending continuity at the top. The piers connect with the deck, making a “quasi-integral” bridge; only the lateral piers are not rigidly fixed to their diaphragm-wall foundations, and use steel–Teflon bearings. The typical deck cross section is conceived as a single-cell torsion-resistant shell, its wing shape stiffened only by reticular internal diaphragms. The orthotropic plate at the end of the deck, stiffened by channel-shaped ribs, reaches relevant width at the site of connection with side access lanes, which are served by similar smaller decks.

On kinetic theory methods in vehicular flow

Similarly to the treatment of diluted gases, kinetic methods are formulated for the study of unidirectional freeway traffic. From these it is possible to construct fluid-dynamic equations which in comparison with heuristic fluid-dynamic models have the advantage of just some adjustable parameters although they have some other restrictions. In this work the comparison between two macroscopic models which are based on a kinetic traffic equation is shown. On the other hand, there will be presented some advances to attempt to generalize some restrictions of the kinetic formulation in order to study the synchronization phenomena, which is a very interesting transitory phase between free flow and traffic jams.

Planning of mobility and parking. The acting of the Urban Mobility Plan

In the urban areas the mobility system is strategic for its working and it is composed of a series of territorial closely interrelated elements. Among these the parking is one of the most important and its organization is a key point of an appropriate planning of mobility: this importance is mainly due to its character of attractor of vehicular flows. The structure of large and medium sized Italian cities imposes many constraints to the creation and the use of parking areas for their impact on the urban livability; the problem is the organization of the whole city, the correct location of the areas and the opportunity to regulate the access to certain areas: in fact the programming of parking areas can have strong repercussions on the city. Another element can be considered: the choice to build parking areas in the center of the towns is in logical conflict with the traffic limiting policies, because the infrastructure, if built, can be used and the investment must be repaid; on the other hand, the decision that some sensitive areas should not be affected by parking infrastructure produces the necessity to strengthen other public services: the question is not only physical (space availability), but it is related with the distribution of opportunities and equipments, so if the center is better served by public transport, the periphery must be served by other infrastructures. As said, the choice of sites for parking’s location and the determination of their operating characteristics can have strong impacts on the organization and the livability of the city itself; it follows the necessity of a close connection with the urban planning and an attention to the morphological characters of the different parts of the city. The tools for planning the mobility and, within it, the parking system, are several. The Urban Mobility Plan is the newest among them; it is a strategic tool because its effects are gathered on the system as a whole and it assumes an overall rationalization and development of networks and vehicles. The paper deepens the characters of this tool, starting from the legislative forecasts, and thereafter on the basis of case-studies. The first part analyses the notions connected with the urban structure, the mobility and the parking system. In the second step the prescriptive aspects are analyzed: the Urban Mobility Plan and the Urban Parking Program are deepen in relation with their main aspects and in relation whit the parking problems. The third part analyses two case-studies; the cases highlights the different application philosophy, in particular for the connection between urban areas and parking system. At least, in the fourth part, are analyzed techniques and tools for solving the parking’ problem, the different modalities for its organization and the management techniques aimed at encouraging more correct behaviors in relation to the different urban areas.

Vehicle Type–Specific Headway Analysis Using Freeway Traffic Data

The distribution of time headway has long been a research topic because headway between vehicles is an important flow characteristic affecting safety, level of service, driver behavior, and capacity of a transportation system. However, almost all reported research on headway is focused on mixed vehicular flow without considering the difference in headway with respect to different vehicle types. In this paper, with the use of 1-day freeway traffic data from Interstate 35 in Austin, Texas, four time headway types based on different combinations of leading vehicles and following vehicles–-car–truck, truck–car, truck–truck, and car–car–-are analyzed at different traffic flow levels. Statistical comparisons between each vehicle type–specific headway and mixed vehicle–type headway are made to verify their significant differences. The paper demonstrates the necessity of vehicle type–specific headway study. The results of the paper not only identify qualitative differences between the vehicle type–specific headways and distributions, but also can be used as a reference for practical applications, especially for improving microscopic traffic simulation models.

Light Controlled Intersection Model Based on the Continuous Petri Net

We propose a light controlled intersection model based on a constant speed continuous Petri net. The Model is innovative, firstly, by the free space modeling together with the opposite direction of the vehicular flow, secondly by the continuous Petri net use only leading to a smaller state space. For this purpose, we show a new method for conflict resolution in a Petri net based on the maximal speed proportion. The model is compared with intersection model based on a classical discrete Petri net and it is evaluated in the simulation where real traffic data is used for the incoming flow.

Effect of rear slant angle on flow structures, and pollutant dispersion and concentration fields in the wake of the studied model vehicle

Experimental investigations of the interaction effect of rear slant angle (i.e., α = 25° and 60°) and heated air exhaust jet condition (i.e., U j and T j ) on flow structures, and pollutant (i.e., scalar) dispersion and concentration fields in the near-wake region of two simplified scale-model vehicles at Reynolds number Re h = 5.8 × 10 4 were performed in a closed-circuit wind tunnel using laser Doppler anemometry (LDA) and the cold wire thermometry. The results show that the behaviors of flow structures and pollutant dispersion in the near-wake region of the studied model vehicles are highly dependent on the interaction effect of U j / U ∞ and α. For the low value of U j / U ∞ (i.e., the driving mode from 30 km h −1 to 70 km h −1), the wake structure of the two studied model vehicles is almost similar to the case without introducing the vehicular exhaust jet flow, U j / U ∞ = 0, but the scalar concentration is neither sent straight to the wake region nor trapped by the recirculation zone. For higher value of U j / U ∞ (i.e., the driving mode of 10 km h −1), the jet flow perturbation along the central plane of the vehicular exhaust tailpipe causes the disappearance of the lower vortex in the recirculation zone for the studied model vehicle A ( α = 25°) while it causes the stretching of the recirculation zone for the studied model vehicle B ( α = 60°). The contaminant is mainly straight trajectory along its jet exhaust flow axis. Outside the recirculation zone, the flow field becomes symmetrical and its flow structure depends only on the rear slant angle of the studied model vehicle. The scalar concentration field of the studied model vehicle B is characterized by a two-dimensional flow structure whatever the studied driving modes are. The distribution of the mean normalized temperature excess field (i.e., scalar concentration field) conforms to the velocity vector field for both studied model vehicles. For the studied model vehicle A, the scalar concentration is drawn to the edge of the trailing vortex at the vehicular exhaust jet side. This phenomenon causes a significant reduction of the scalar concentration level whatever the studied driving modes are.

Traffic jams without bottlenecks—experimental evidence for the physical mechanism of the formation of a jam

A traffic jam on a highway is a very familiar phenomenon. From the physical viewpoint, the system of vehicular flow is a non-equilibrium system of interacting particles (vehicles). The collective effect of the many-particle system induces the instability of a free flow state caused by the enhancement of fluctuations, and the transition to a jamming state occurs spontaneously if the average vehicle density exceeds a certain critical value. Thus, a bottleneck is only a trigger and not the essential origin of a traffic jam. In this paper, we present the first experimental evidence that the emergence of a traffic jam is a collective phenomenon like ‘dynamical’ phase transitions and pattern formation in a non-equilibrium system. We have performed an experiment on a circuit to show the emergence of a jam with no bottleneck. In the initial condition, all the vehicles are moving, homogeneously distributed on the circular road, with the same velocity. The average density of the vehicles is prepared for the onset of the instability. Even a tiny fluctuation grows larger and then the homogeneous movement cannot be maintained. Finally, a jam cluster appears and propagates backward like a solitary wave with the same speed as that of a jam cluster on a highway.

Simulation of bi-directional pedestrian flow based on cellular automata model

Simulations of bi-directional pedestrian flow with different direction splits and system sizes are presented based on cellular automata (CA) in this paper. It is well known that pedestrian movement is more flexible and adaptive to the dynamic conditions than vehicular flow, so four dynamic parameters are formulated to simplify tactically the decision-making process of pedestrians, which can reflect the pedestrian's judgment on the surrounding conditions and decide his her choice of action. The relationships of velocity-density and volume-density at different direction splits and on the different size system are studied and analyzed. It is found that there are phase transitions and a critical density point in the model and the relationships of velocity-density and volume-density are different in different phases. And the ratio of direction splits and system size affect the shapes of velocity-density curve, volume-density curve and the value of critical density point.

‘Slicing Through Space’

Providing for the movement of people and things is an inevitable and increasingly important element of urban governance. Urban life in Australian cities has been physically structured around the private motor vehicle, and transport policies have historically focused on the public funding of large-scale public roadways. There is no better example of this approach to transport planning than in Southeast Queensland, where government departments associated with responsibilities for road infrastructure have traditionally wielded enormous power, and have repeatedly attempted to impose large-scale technological solutions for transport problems without regard for their wider impacts on urban life. Despite an emerging awareness of the need to reduce carbon emissions by establishing alternative models of urban mobility, local authorities in Brisbane have recently followed in this well- established tradition by embarking on an ambitious expansion of river crossings and underground road tunnels as a way to increase the capacity of private vehicular flows through the inner city. This article is an exploration of the philosophical framework ‘driving’ these political decisions and their inevitable imposition of new spatio-temporal laws on Brisbane’s inhabitants. Drawing on Henri Lefebvre’s account of the relationship between the production of space and social rhythms, it is argued that these transport planning decisions and the way they govern mobility will reproduce the destructive effects of abstraction on both space and the rhythms of the city.

Simulation of pedestrian flow on square lattice based on cellular automata model

Simulations of two-way and four-way pedestrian flow on the square lattice for small systems will be presented based on cellular automata (CA) in this paper. For the reason that the decision-making process of pedestrians in their movements is complex and intelligent, pedestrian movement is more flexible and adaptive to dynamic conditions than vehicular flow. First, a special technique will be introduced to simplify tactically the process into the interaction of four dynamic parameters, which can reflect the pedestrian judgment on the surrounding conditions and decide the pedestrian's choice of action such as moving ahead, stopping to wait, position exchange, lane switching, back stepping, etc. Second, the simulation method and the relationships of velocity–density and flow–density will be studied and analyzed. It is found that there are phase transitions at the critical density point and at different phases the relationships of velocity–density and flow–density are different from each other. Moreover, the different weight coefficients of four dynamic parameters affect the simulation results of these two models.

From Axial to Road-Centre Lines: A New Representation for Space Syntax and a New Model of Route Choice for Transport Network Analysis

Axial analysis is one of the fundamental components of space syntax. The space syntax community has suggested that it picks up qualities of configurational relationships between spaces not illuminated by other representations. However, critics have questioned the absolute necessity of axial lines to space syntax, as well as the exact definition of axial lines. Why not another representation? In particular, why not road-centre lines, which are easily available in many countries for use within geographical information systems? Here I propose that a recently introduced method of analysis, angular segment analysis, can marry axial and road-centre line representations, and in doing so reflect a cognitive model of how route choice decisions may be made. I show that angular segment analysis can be applied generally to road-centre line segments or axial segments, through a simple length-weighted normalisation procedure that makes values between the two maps comparable. I make comparative quantitative assessments for a real urban system, not just investigating angular analysis between axial and road-centre line networks, but also including more intuitive measures based on metric (or block) distances between locations. I show that the new angular segment analysis algorithm produces better correlation with observed vehicular flow than both standard axial analysis and metric distance measures. The results imply that there is no reason why space syntax inspired measures cannot be combined with transportation network analysis representations in order to create a new, cognitively coherent, model of movement in the city.

Influence of Bicycle Traffic on Capacity of Typical Signalized Intersection

Bicycle traffic has a significant effect on the capacity of signalized intersections. This paper divides the influence of bicyclists on vehicular flow into four types with the time durations estimated based on probability, shock wave, and gap acceptance theory. Vehicular saturation flow rate is predicted for various conditions on the basis of the speed-flow curve for the capacity of typical intersections influenced by bicycle traffic. The model overcomes the limitations of the Highway Capacity Manual (HCM, 2000) method for left-turns due to data collection, and takes into account the effect of trapped bicycles on the through vehicular traffic. The numerical results show that the left-turn and through capacities predicted by the model are lower than those of the HCM method. The right-turn capacity is close to that of the HCM method at low bicycle volumes and higher than that of the HCM method at high bicycle volumes.

IMPACT OF REAL-TIME INFORMATION ON DYNAMIC VEHICULAR FLOWS UNDER MIXED TRAFFIC CONDITIONS

This research aims at studying impacts of real-time information on mixed traffic flows through an integrated dynamic simulation-assignment model, DynaTAIWAN. The DynaTAIWAN model is composed of 2 layers, namely simulation-layer and real-time control layer. The simulation layer is designed to simulate traffic flow patterns according to assumed tripmaker characteristics and/or under a set of given conditions; the real-time control layer receives real-time vehicle information and forecast short-term traffic flow patterns. In the simulation process, each vehicle is moved and tracked individually. Four different vehicle types are explicitly considered in DynaTAIWAN, including car, bus, motorcycle, and truck. Vehicles are moving along the link through macroscopic flow relationships, speeds of each type of vehicle are adjusted. Numerical experiments based on real-time information are conducted in a 50-node test network and a Taichung City Network.

Estimation of the minimum integration time for determining the equivalent continuous sound level with a given level of uncertainty considering some statistical hypotheses for road traffic

In this work a relation is obtained for calculating the minimum time necessary for measuring the hourly equivalent level, with preset uncertainty on the L eq in the case of noise produced by road traffic under different statistical hypotheses for vehicular flow. A simple equivalent level prediction model is used as reference. Some specific relations between acoustic power and vehicle speed are implemented in this model. Through the application of the classic theory of errors, the expression for the uncertainty on the L eq is obtained with reference, in particular, to various vehicle distributions: uniform (rectangular), triangular, normal and Poisson that, according to the available information, can be applied for describing traffic flow. Uncertainties over the distance source/receiver and speed of the vehicles are also taken into consideration in the calculation of uncertainty on L eq . The minimum measurement time is obtained from the expression of the error associated with the L eq , according to the hourly number of vehicles, so that the uncertainty on the L eq stays within a preset value. In this case too, the determination of the minimum time refers to the various previously mentioned hypotheses with respect to vehicle distribution. It is shown that it is possible to obtain a correct description of road traffic noise, within a predetermined uncertainty on the hourly L eq , by measuring over times considerably shorter than an hour.

Motorway traffic parameter estimation from mobile phone counts

In this paper a new method for real time estimation of vehicular flows and densities on motorways is proposed. This method is based on fusing traffic counts with mobile phone counts. The procedure used for the estimation of traffic flow parameters is based on the hypothesis that “instrumented” vehicles can be counted on specific motorway sections and traffic flow can be measured on entrance and exit ramps. The motorway is subdivided into cells, assuming that mobile phones entering and exiting every cell can be counted during the observation period. An estimate of “instrumented” vehicle concentration is obtained and propagated on the network in time and space. This allows one to estimate traffic flow parameters by sampling “instrumented” traffic flow parameters using a “concentration” (the ratio of the densities of instrumented vehicles to the density of overall traffic) propagation mechanism.

An analysis of the spatial structure of a new desert town: Al Ain, United Arab Emirates

This paper presents a study of the current spatial structure of Al Ain, a town-oasis in the United Arab Emirates, by examining the relationship between spatial design and circulation patterns within the town. An analysis of vehicular and pedestrian flows was carried out to establish the relationship between attractors, accessibility and configuration of road network. The main objective was to test Space Syntax methodology in order to explore design guidelines as well as re-design proposals if some areas are found to be very deficient in terms of spatial layout and ease of movement and connectivity. URBAN DESIGN International (2006) 11, 3–19. doi:10.1057/palgrave.udi.9000155