Faculty Publications

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    Estimation and Comparison of Saturation Flow at Signalized Intersection in Mixed Traffic Condition
    (Springer Science and Business Media Deutschland GmbH, 2022) Mahapatra, M.J.; Advani, M.; Ravi Shankar, A.U.
    Signalized intersections are the important part of urban road network. Capacity of signalized intersections has significant role in capacity of overall road network in an area. Accordingly, capacity estimation of signalized intersection and therefore the estimation of saturation flow values become an important aspect especially for Indian roads due to the presence of different types of vehicles and space sharing-based vehicular movement. This study extracts the saturation flow from the field data captured through videography and compares it with the saturation flow values estimated by various methods available in literature. Data have been collected at two signalized intersections; first one is a four-legged intersection, and other one is three-legged intersection. Approach width of all arms of both intersections ranges from 7.6 to 10.3 m. Both intersections are located on the main arterial road of Delhi, India, and at the distance of 1.1 km without any obstructions in-between. Saturation flow has been estimated through existing methods available in literature and compared with the developed model in this study. Proposed model indicates that with the increased width, saturation flow values also increase. Values estimated are closer to values obtained by Webster’s method. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
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    Impact of Leading Vehicles of the Queue on Saturation Flow at Signalized Intersections
    (Springer Science and Business Media Deutschland GmbH, 2024) Kumar, R.; Mohan, M.
    Saturation flow is an essential component in the design and capacity estimation of signalized intersections. The saturation flow rate is influenced by several factors, including intersection geometry, speed limit, the proportion of heavy vehicles, parking activities, bus stops adjacent to the intersection area, lane utilization, pedestrian volume, etc. Estimation of saturation flow is well-established for homogeneous traffic conditions. However, measuring and modelling saturation flow are challenging in mixed traffic conditions due to the non-lane-based traffic flow and the presence of multiple types of vehicles. Typically, Passenger Car Unit (PCU) adopted should be enough to account for the variation among the vehicles that constitute the queue while estimating saturation flow. However, field observation at Indian intersections indicated that the vehicles at the front of the queue might profoundly influence the queue discharge at the onset of green phase, thereby exposing the shortcoming of PCUs. This influence is clearly visible when heavy vehicles make up the front of the queue and owing to their inferior operational performance and larger size, they deny the following vehicles the opportunity to attain their desired acceleration. To investigate this, the present study simulated the operation of a typical four-legged signalized intersection in VISSIM software. The subsequent analysis revealed a strong relationship between leaders of the queue and the saturation flow of the approach. This result from the simulation was then verified based on field data. The study concluded that the PCU factors adopted at signalized intersections fail to account for the effect of the queue leader’s composition, which has a marked influence on the saturation flow. © 2024, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
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    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.
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    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.
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    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).
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    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.
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    Investigating bus stops' influence on saturation flow at signalized intersections in heterogeneous traffic
    (Aracne Editrice, 2022) Shubhashree, K.S.; Mohan, M.
    The public transportation system efficiently reduces congestion and pollution as they lessen the dependency on personalized modes. However, most bus stops are located close to the intersection, and the stopping buses often create a bottleneck. At signalized intersections, this will seriously impact the saturation flow as it hinders the efficient functioning of the traffic signal system, resulting in delays and reduction of the intersection's capacity. Hence, a profound understanding of the factors associated with bus stoppages, which influence the saturation flow, is essential in designing efficient signalized intersections. This study simulates traffic flows at signalized intersections in heterogeneous traffic in a micro-simulation software VISSIM. Results of multiple simulation run indicated that saturation flow at intersections depends on the percentage of buses in the vehicular mix, the distance of bus stop from the stop line, and percentages of right and left-turning traffic. Further, the study proposes separate saturation flow models for upstream and downstream bus stop conditions. These could be used to optimally place bus stops near the intersection such that it does not hamper the performance of the intersection while not causing any undue discomfort to the bus passengers. © 2022, Aracne Editrice. All rights reserved.