Keywords: DLR Reference EPFL-CONF-155461 Record created on 2010-11-23, modified on 2016-08-08

/pdf/simulation-of-urban-mobility-3yunecxhhi.pdf

Simulation of Urban Mobility

This paper describes a modeling methodology adopted to simulate the flow of heterogeneous traffic with vehicles of wide ranging static and dynamic characteristics. The simulation framework for the traffic-flow model was prepared in such a way that the absence of lane discipline in mixed traffic flow conditions is taken into account. A detailed structure of the proposed model is presented. Common issues related to traffic simulation such as vehicle generation, logics for vehicular movement, etc., are described in detail in the context of heterogeneous traffic conditions. The paper also discusses the procedures adopted for validation of the proposed model and their outcomes. Finally, the details of application of the model to study the traffic flow characteristics on urban roads are also presented.

Methodology for Modeling Highly Heterogeneous Traffic Flow

Acceleration/deceleration (A/D) behaviour of vehicles is important for various applications like length of yellow light at inter- section, determination of sight distances at intersection, determination of length of A/D lanes, ramp design, traffic simulation modelling, vehicular emission modelling, instantaneous fuel consumption rate modelling, etc. Literature reports A/D studies for cars in lane disciplined homogeneous traffic. However, Indian traffic stream is weak lane disciplined and heterogenous, containing various vehicle types like truck, motorized three and two wheeler and diesel and petrol driven cars. Also, the reported studies are based on out of date data, collected using traditional and less accurate methods. Hence, this work aims to study the A/D behaviour of various vehicle types using modern instruments like Global Positioning System (GPS) in controlled manner including maximum A/D envelop. It is observed that acceleration rates of vehicles observed in this study, differed from acceleration rates reported in literature. On finding existing acceleration models insufficient to explain the acceleration behaviour of vehicles observed in this study, new models have been proposed and validated using statistical tools. Acceleration behaviour of cars varied with the change in gears, though the pattern remained similar in all gears.

Acceleration-Deceleration Behaviour of Various Vehicle Types

The interplay between congestion and crowding externalities in the design of urban bus systems is identified and analysed. A multimodal social welfare maximisation model with spatially disaggregated demand is developed, in which users choose between travelling by bus, car or walking in a transport corridor. Optimisation variables are bus fare, congestion toll, bus frequency, bus size, fare collection system, bus boarding policy and the number of seats inside buses. We find that optimal bus frequency results from a trade-off between the level of congestion inside buses, i.e., passengers’ crowding, and the level of congestion outside buses, i.e., the effect of frequency on slowing down both buses and cars in mixed-traffic roads. A numerical application shows that optimal frequency is quite sensitive to the assumptions on crowding costs, impact of buses on traffic congestion, and overall congestion level. If crowding matters to users, buses should have as many seats as possible, up to a minimum area that must be left free of seats. If for any other reason planners decide to have buses with fewer seats than optimal (e.g., to increase bus capacity), frequency should be increased to compensate for the discomfort imposed on public transport users. Finally, the consideration of crowding externalities (on both seating and standing) imposes a sizeable increase in the optimal bus fare, and consequently, a reduction of the optimal bus subsidy.

http://repositorio.uchile.cl/bitstream/handle/2250/126546/Multimodal-pricing-and-optimal-design-of-urban-public-transport-The-interplay-between-traffic-congestion-and-bus-crowding.pdf?sequence=1

Multimodal pricing and optimal design of urban public transport: The interplay between traffic congestion and bus crowding

A significant part of the world, especially in most of the Asian countries, has heterogeneous traffic characterized by diverse vehicles, changing composition, lack of lane discipline, etc., resulting in a very complex behavior. Microsimulation is, therefore, highly suited to model such traffic. However, these models need to be calibrated before their application. Although several studies have been reported in the literature on the methodologies for calibration, all of them have focused on homogeneous traffic conditions having good lane discipline. In highly heterogeneous traffic, several other factors such as traffic composition and static and dynamic characteristics of vehicles have to be considered in the calibration process. Moreover, side-by-side stacking of vehicles across the road width occurring in the absence of lane discipline should also be modeled. Hence, a methodology for representing nonlane-based driving behavior and calibrating a microsimulation model for highly heterogeneous traffic at signalized intersection is proposed. Calibration parameters were identified using sensitivity analysis, and the optimum values for these parameters were obtained by minimizing the error between the simulated and field delay using genetic algorithm. The proposed methodology is illustrated using Verkehr in Staedten simulation, a widely used psychophysical car-following model based microsimulation software. Signalized intersections having diverse traffic and geometric characteristics from two cities of India are taken as a case study.

Calibration of Microsimulation Models for Nonlane-Based Heterogeneous Traffic at Signalized Intersections

The number and type of bus stops provided on a road significantly influence the flow characteristics of traffic on the road. The study of the influence of bus stops on traffic flow under homogeneous traffic conditions has been attempted by several researchers. However, studies on the influence of bus stops on traffic flow under heterogeneous traffic conditions, are found to be absent. This paper is concerned with the study of heterogeneous traffic flow characteristics using a simulation technique with specific reference to the influence of bus stops on the traffic flow. First, an overview of the microscopic traffic-flow simulation model used to study the flow characteristics of nonlane-based heterogeneous traffic on urban road links is given. Then, the validation of the model based on field observed data is described. Finally, the application of the model to study the impact of curbside bus stops and bus bays on the speeds of other vehicles in heterogeneous traffic streams is dealt with. The effects of variation of the basic parameters, such as bus dwell time, road width, and traffic flow level, are examined for both curbside and bus bay type of stops. The usefulness of the model in fixing the traffic flow levels for replacing curbside stops with bus bays, as example, has also been highlighted.

Influence of Bus Stops on Flow Characteristics of Mixed Traffic

This paper describes an attempt made to study the time-headway distribution of urban heterogeneous traffic over a wide range offlow levels. An appropriate methodology for the collection and extraction of headway data has been suggested. The importance of a systematic procedure for grouping of headway data through appropriate choice of class interval has been discussed. The methodology for choice of best fitting statistical distribution to the observed headway data has also been described. The result of the study has shown that, the headways of urban mixed-traffic dominated by smaller vehicles like motorised two-wheelers can be modelled using negative exponential distribution over a wide range of traffic flow levels.

Headway distribution of heterogeneous traffic on urban arterials

The important aspect that makes the nature of traffic flow stochastic is the randomness inherent in road user (driver) and vehicular characteristics. We give an overview of the development, validation and use of a stochastic traffic-flow simulation model for urban highways with heterogeneous traffic. An appropriate methodology for the collection and extraction of headway data has been suggested. The headways of urban mixed-traffic dominated by smaller vehicles like motorized two-wheelers can be modeled using negative exponential distribution over a wider range of traffic flow. An attempt has also been made to model the traffic flow on a road stretch with bus stops. The random natures of the arrival pattern and dwell time of the buses have been suitably incorporated

Modeling stochasticity of heterogeneous traffic

Emulsion-Treated Base (ETB) is one of the most preferred base layer stabilization methods in which dense graded aggregates are treated with a slow setting bituminous emulsion. To reduce the cost of ETB and minimize the need for virgin aggregates, it is essential to evaluate the possibility of incorporating higher dosages of Reclaimed Asphalt Pavement material (RAP) in ETB. The present study evaluates the effect of RAP incorporation in ETB at dosages of 0%, 25%, 50%, 75%, and 100%. The effects of RAP incorporation were studied in terms of RAP mixing and RAP blending methods. RAP mixing is a process in which a definite proportion of RAP is added to virgin aggregates of a given gradation without a target gradation, while in RAP blending, virgin aggregates of required aggregate sizes are blended to RAP with the objective of achieving a targetted dense aggregate gradation. In this study, RAP was characterized using cohesion tests, fragmentation tests, and other physical properties recommended by the International Union of Laboratories and Experts in Construction Materials, Systems, and Structures (RILEM) Technical Committee. When 50% RAP was added to ETB using the RAP mixing method, the Maximum Dry Density (MDD) of the mix decreased by 4.4%, but in using RAP blending, the reduction in MDD was only 1.3%. ETB prepared with up to 75% RAP, 3% emulsion, and 1% cement, using the RAP blending method, was found to satisfy the minimum indirect tensile strength requirement of 225 kPa (specified by TG 2 2009 and IRC 37 2012), and exhibited appreciable rutting resistance and a tensile strength ratio of more than 0.7. This study identified that 50% RAP incorporation in ETB using blending gives the best performance in terms of cohesive and adhesive strength, moisture resistance, and resistance to permanent deformation. 

Reebu Zachariah Koshy

Papers

Methodology for Modeling Highly Heterogeneous Traffic Flow

Influence of Bus Stops on Flow Characteristics of Mixed Traffic

Headway distribution of heterogeneous traffic on urban arterials

Modeling stochasticity of heterogeneous traffic

Laboratory Evaluation of Emulsion-Treated Base Layer Mixes Incorporating Reclaimed Asphalt Pavement Materials