Journal Articles
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Item Review of Methods for Estimation of Passenger Car Unit Values of Vehicles(American Society of Civil Engineers (ASCE) onlinejls@asce.org 1801 Alexander Bell DriveGEO Reston VA 20191 Alabama, 2019) Raj, P.; Sivagnanasundaram, K.; Asaithambi, G.; Ravi Shankar, A.U.Estimation of passenger car unit (PCU) values is very important for traffic capacity analysis and other relevant applications such as level of service (LOS) measures, determination of saturation flow rate, signal design and coordination, and development of traffic flow models. Because of such wide applications, the accuracy of PCU values is highly significant in traffic flow analysis. Many research works have been carried out on estimation of PCUs in the past few decades. In developed countries, various methods were developed for estimating PCU values for different types of facilities which carry trucks and buses of lesser composition. But these methods are not completely analogous for mixed traffic due to the presence of wide variety of vehicle types, nonlane discipline, intraclass variability of vehicles and their maneuverability. With this consideration, various methods used for estimating PCUs for different facility types under homogeneous and mixed traffic conditions are reviewed and the drawbacks of the existing methods are identified in this paper. The challenges in estimating PCU values and future directions for improving the PCU estimation methods are also presented. © 2019 American Society of Civil Engineers.Item Study of unique merging behavior under mixed traffic conditions(Elsevier Ltd, 2015) Kanagaraj, V.; Srinivasan, K.K.; Sivanandan, R.; Asaithambi, G.Roads in developing countries carry mixed traffic with wide variations in static and dynamic characteristics of vehicles. The traffic flow is also generally devoid of lane discipline, with vehicles occupying any available road space ahead. In such a regime of traffic flow, the phenomena of merging of vehicles at intersections of two roads is complex, warranting further study. The merging maneuvers at T-intersections under congested traffic conditions were studied microscopically through video-recording. In congested situations, the merging vehicle attempts a complex merging maneuver to enter the main traffic stream. Two unique merging processes are commonly observed in mixed traffic: group and vehicle cover merging (these are generally not observed in countries such as US). The author is using these words first time in this study. These reflect the different types of driver behavior - merging in groups, and by taking cover of another vehicle. Probabilistic models for group and vehicle cover merging are developed that capture this unique merging behavior. Comprehensive microscopic data collection and extraction were carried out to study the merging process at T-intersection under congested conditions. Merging models were then estimated using maximum likelihood method with disaggregate data that was collected for a case study T-intersection in Chennai city, India. Such models can find applications in simulation of highly congested traffic flow in a realistic manner under mixed traffic conditions. They can also give insights on devising better traffic control measures at such intersections. © 2015 Elsevier Ltd.Item Trajectory data and flow characteristics of mixed traffic(National Research Council, 2015) Kanagaraj, V.; Asaithambi, G.; Toledo, T.; Lee, T.-C.Models of driving behavior (e.g., car following and lane changing) describe the longitudinal and lateral movements of vehicles in the traffic stream. Calibration and validation of these models require detailed vehicle trajectory data. Trajectory data about traffic in cities in the developing world are not publicly available. These cities are characterized by a heterogeneous mix of vehicle types and by a lack of lane discipline. This paper reports on an effort to create a data set of vehicle trajectory data in mixed traffic and on the first results of analysis of these data. The data were collected through video photography in an urban midblock road section in Chennai, India. The trajectory data were extracted from the video sequences with specialized software, and the locally weighted regression method was used to process the data to reduce measurement errors and obtain continuous position, speed, and acceleration functions. The collected data were freely available at http://toledo .net.technion.ac.il/downloads. The traffic flow characteristics of these trajectories, such as speed, acceleration and deceleration, and longitudinal spacing, were investigated. The results show statistically significant differences between the various vehicle types in travel speeds, accelerations, distance keeping, and selection of lateral positions on the roadway. The results further indicate that vehicles, particularly motorcycles, move substantially in the lateral direction and that in a substantial fraction of the observations, drivers are not strictly following their leaders. The results suggest directions for development of a driving behavior model for mixed traffic streams. © © 2015 National Academy of Sciences. All rights reserved.Item Evaluation of right-turn lanes at signalized intersection in non-lane-based heterogeneous traffic using microscopic simulation model(Maney Publishing michael.wagreich@univie.ac.at, 2015) Asaithambi, G.; Sivanandan, R.In developing countries like India, the traffic on urban roads is highly heterogeneous in nature, with vehicles of widely varying static and dynamic characteristics. This type of traffic is characterized by lack of queue and lane discipline (lane-less movement) based on availability of spaces near intersections. Moreover, at intersections, straight-through, left-, and right-turning vehicles seek to occupy the same physical space. In such situations, the through vehicles are susceptible to delays in the absence of turn lanes for the left-turning and right-turning vehicles and vice versa. Models suitable for analysis of such traffic flow hardly exist, and most of the available models are limited in scope. In the current study, a microscopic traffic simulation model for signalized intersection is developed specifically for heterogeneous traffic. This model covers different vehicle types and allows for some special behavior, such as seepage of two-wheelers to fronts of queues. Detailed study of queue formation and dissipation were done microscopically under non-lane-based traffic conditions near intersection area. The model was calibrated and tested with data from Chennai city, India, and its predictions were found to be in close agreement with the field data. In addition, the model makes a significant contribution to the study of right-turn lane (RTL) on delays to vehicles. In general, RTL is found to be advantageous for most cases of approach volumes and right-turn proportions. The optimal lengths of RTL are suggested for various approach volumes and right-turn proportions. © 2015 W. S. Maney & Son Ltd.Item Microscopic simulation for modeling exclusive stopping space for motorcycles under non-lane based mixed traffic conditions(Institute for Transport Studies in the European Economic Integration, 2015) Asaithambi, G.; Kumar, R.V.Y.; Sivanandan, R.Mixed traffic flow with high composition of motorcycles is a common situation in many urban areas in South Asian countries like India. It consists of vehicles having diverse static and dynamic characteristics. This type of traffic is characterized by lack of queue and lane disciplines. Motorcycles, due to their smaller size, have greater freedom to manoeuver in a mixed traffic stream. They tend to accumulate near the stop line by weaving through gaps between other vehicles during the red phase. The provision of Exclusive Stopping Space for Motorcycles (ESSM) near the stop line is believed to be beneficial in discharging the motorcycles faster, thereby enhancing the efficiency of the intersection. A microscopic traffic simulation model for a signalized intersection developed specifically for mixed traffic was used in this study. The model was calibrated and tested wit h dat a from Chennai city, India. This model was used to simulate traffic flow at an intersection assuming the presence of ESSM. The efficacy of ESSM was evaluated by varying the vehicular composition, traffic volume and ESSM lengths. The findings show that for certain composition, volume levels and lengths of ESSM, delays to vehicles decrease, thereby indicating its benefits. © 2015 European Transport\Trasporti Europei.Item Evaluation of Intersection Traffic Control Measures through Simulation(Springer India sanjiv.goswami@springer.co.in, 2015) Asaithambi, G.; Sivanandan, R.Modeling traffic flow is stochastic in nature due to randomness in variables such as vehicle arrivals and speeds. Due to this and due to complex vehicular interactions and their manoeuvres, it is extremely difficult to model the traffic flow through analytical methods. To study this type of complex traffic system and vehicle interactions, simulation is considered as an effective tool. Application of homogeneous traffic models to heterogeneous traffic may not be able to capture the complex manoeuvres and interactions in such flows. Hence, a microscopic simulation model for heterogeneous traffic is developed using object oriented concepts. This simulation model acts as a tool for evaluating various control measures at signalized intersections. The present study focuses on the evaluation of Right Turn Lane (RTL) and Channelised Left Turn Lane (CLTL). A sensitivity analysis was performed to evaluate RTL and CLTL by varying the approach volumes, turn proportions and turn lane lengths. RTL is found to be advantageous only up to certain approach volumes and right-turn proportions, beyond which it is counter-productive. CLTL is found to be advantageous for lower approach volumes for all turn proportions, signifying the benefits of CLTL. It is counter-productive for higher approach volume and lower turn proportions. This study pinpoints the break-even points for various scenarios. The developed simulation model can be used as an appropriate intersection lane control tool for enhancing the efficiency of flow at intersections. This model can also be employed for scenario analysis and can be valuable to field traffic engineers in implementing vehicle-type based and lane-based traffic control measures. © 2015, The Institution of Engineers (India).Item Analysis of occupation time of vehicles at urban unsignalized intersections in non-lane-based mixed traffic conditions(Springer Berlin, 2016) Asaithambi, G.; Anuroop, C.In India, traffic flow on roads is highly mixed in nature with wide variations in the static and dynamic characteristics of vehicles. At unsignalized intersections, vehicles generally do not follow lane discipline and ignore the rules of priority. Drivers generally become more aggressive and tend to cross the uncontrolled intersections without considering the conflicting traffic. All these conditions cause a very complex traffic situation at unsignalized intersections which have a great impact on the capacity and performance of traffic intersections. A new method called additive conflict flow (ACF) method is suitable to determine the capacity of unsignalized intersections in non-lane-based mixed traffic conditions as prevailing in India. Occupation time is the key parameter for ACF method, which is defined as the time spent by a vehicle in the conflict area at the intersection. Data for this study were collected at two three-legged unsignalized intersections (one is uncontrolled and other one is semicontrolled) in Mangalore city, India using video-graphic technique during peak periods on three consecutive week days. The occupation time of vehicles at these intersections were studied and compared. The data on conflicting traffic volume and occupation time by each subject vehicle at the conflict area were extracted from the videos using image processing software. The subject vehicles were divided into three categories: two wheelers, cars, and auto-rickshaws. Mathematical relationships were developed to relate the occupation time of different categories of vehicles with the conflicting flow of vehicles for various movements at both the intersections. It was found that occupation time increases with the increasing conflicting traffic and observed to be higher at the uncontrolled intersection compared to the semicontrolled intersection. The segregated turning movements and the presence of mini roundabout at the semicontrolled intersection reduces the conflicts of vehicular movements, which ultimately reduces the occupation time. The proposed methodology will be useful to determine the occupation time for various movements at unsignalized intersections. The models developed in the study can be used by practitioners and traffic engineers to estimate the capacity of unsignalized intersections in non-lane-based discipline and mixed traffic conditions. © 2016, The Author(s).Item Passenger car unit estimation at signalized intersection for non-lane based mixed traffic using microscopic simulation model(Budapest University of Technology and Economics office@pp.bme.hu Budafoki ut 4 Budapest H-1111, 2017) Asaithambi, G.; Mourie, H.S.; Sivanandan, R.In India, traffic on roads is mixed in nature with widely varying static and dynamic characteristics of vehicles. At intersections, vehicles do not follow ordered queue and lane discipline. Different vehicle types occupy different spaces on the road, move at different speeds, and start at different accelerations. The problem of measuring volume of such mixed traffic has been addressed by converting different vehicles categories into equivalent passenger cars and expressing the volume in terms of Passenger Car Unit (PCU) per hour. The accurate estimation of PCU values for different roadway and traffic conditions is essential for better operation and management of roadway facilities. Hence, the objective of the present study is to estimate the PCU values at signalized intersection in mixed traffic and to study the influence of traffic volume, traffic composition and road width on PCU values. For this purpose, a mixed traffic simulation model developed specifically for a signalized intersection was used. The model was calibrated and validated with the traffic data collected from a signalized intersection in Chennai city. Simulation runs were carried out for various combinations of vehicular composition, volume levels and road width. It was observed that presence of heavy vehicles and increase in road width affects the PCU values. The obtained PCU values were statistically checked for accuracy and proven to be satisfied. The PCU values obtained in this study can be used as a guideline for the traffic engineers and practitioners in the design and analysis of signalized intersections where mixed traffic conditions exist.Item Overtaking behaviour of vehicles on undivided roads in non-lane based mixed traffic conditions(Periodical Offices of Chang- an University, 2017) Asaithambi, G.; Shravani, G.Traffic on Indian roads is highly mixed in nature with wide variations in the static and dynamic characteristics of vehicles. These vehicles do not follow strict lane discipline and occupy any available lateral position on the road space. Overtaking is one of the most complex and important manoeuvre on undivided roads where the vehicles use the opposing lane to overtake the slower vehicles with the presence of oncoming vehicles from opposite direction. They are unavoidable especially in the case of mixed traffic conditions where there is always a speed difference between the fast and slow moving vehicles. Overtaking process involves lane-changing manoeuvres, acceleration and deceleration actions and estimation of relative speed of overtaking and overtaken vehicles, and also, estimation of speed and distance of the oncoming vehicle. The main objective of the present study is to study the overtaking characteristics of vehicles on undivided roads under mixed traffic conditions. For this purpose, details of overtaking data were collected on a two-lane two-way undivided road using moving car observer method and registration plate method. The overtaking characteristics of all types of vehicles under mixed traffic conditions were observed and mathematically modelled. The data extracted and analysed were the acceleration characteristics, speeds of the overtaking vehicles, overtaking time, overtaking distances, safe opposing gap required for overtaking, flow rates, overtaking frequencies, types of overtaking strategy, and types of overtaking and overtaken vehicles. Two types of overtaking strategies were observed in the field such as flying overtaking and accelerative overtaking. Graphs were plotted between the relative speed of the overtaking and overtaken vehicles against the overtaking time and negative correlation was found between the speed differential and total overtaking time for all categories of vehicles. It was observed that the number of overtaking increases with increase in the flow rate in the on-going direction and decreases with increase in flow in the opposite direction. The results obtained from this study will be useful to understand the overtaking behaviour of vehicles in mixed and non-lane discipline traffic conditions. These parameters will be useful in the development of traffic simulations models for undivided roads and thereby for estimation of capacity. The findings from the study can also be used to estimate potential collision times which will be helpful to improve the road safety. © 2017 The AuthorsItem Modeling free-flow speeds on undivided roads in mixed traffic withweak lane discipline(SAGE Publications Ltd, 2018) Chathoth, V.; Asaithambi, G.In developing countries like India, transportation systems are characterized by limited roadway infrastructure and lack of operation and management experience. Hence, there exists a need to evaluate a performance indicator that reflects the current level of service (LOS) of a road facility. Free-flow speed (FFS) is a key parameter used to express LOS assessment. The objective of this study is to develop FFS prediction models for undivided roads with mixed traffic conditions in both urban and rural settings in India. Traffic data were collected from two-way two-lane undivided roads in southern India during freeflow traffic conditions using videographic method. Various class-specific and site-specific characteristics, such as vehicle class, subclass, carriageway width, link length, number of side roads, lateral clearance, land use type, and area type, were investigated and their influence on FFS evaluated. Statistical tests assessed the variations of obtained FFS with different vehiclespecific and site-specific factors. Free-flow prediction models were developed using linear regression method. The developed models show that FFS increases with greater carriageway width, lateral clearance, and link length, and decreases with increase in number of side roads. In general, FFS is higher in rural areas than urban areas. Similarly, open areas have higher FFS than residential, institutional, and commercial areas. The model can be used to predict FFS of undivided roads if site-specific and vehicle-specific data are known. This study finds interesting applications in capacity and LOS analysis, accident analysis, and before-and-after studies of road improvement schemes. © National Academy of Sciences: Transportation Research Board 2018.