Identification of platoon dispersion pattern under heterogeneous traffic conditions
Introduction
The problems related to transportation in urban areas occur when systems of transport cannot suffice the needs of urban mobility. The ability of transport system to move people and goods between multiple origins and destinations affect the urban productivity. The most prominent transportation problems such as congestion, consolidated travel demands and crash rates are highly intense at intersections. Intersections are the influential locations in arterial road networks. Installation of proper control measures in the form of traffic signals at intersections play a significant role to minimize accidents and delay and to enhance traffic flow. The pattern of dispersion or spreading out of a platoon as it advances downstream at any section along the roadway enact a significant role in traffic flow modelling and analysis. A platoon formed under road traffic is defined by the Highway Capacity Manual (2010) as “a group of vehicles or pedestrians traveling together as a group, either voluntarily or involuntarily because of signal control, geometrics, or other factors.” The phenomenon of platoon dispersion is defined as the gradual spread out of platoons as they advance downstream. This dispersion is due to the variation in vehicular speeds, interactions due to lane changing or merging and interferences with pedestrians, parked vehicles etc. The platoon dispersion phenomenon under heterogeneous traffic is an intricate process due to the presence of various modes of vehicles, absence of lane discipline, aggressive driver behavior etc. The driver of the following vehicle moves forward constantly with an intention of overtaking with or without lane changing maneuvers. An attempt is made in this work to identify the pattern of platoon dispersion and to locate sections where initial and higher platoon diffusion occur at downstream of traffic signal at different levels of volume based on the speed variability measures such as profiles of speed, standard deviation, relative standard deviation relative speed difference and platoon speed, estimated for various categories of vehicles under heterogeneous traffic conditions. In addition to this various other platoon characterizing variables like critical inter arrival time, inter–platoon arrival time, intra–platoon arrival time and platoon size are also studied.
Section snippets
Literature review
Several studies on dispersion of platoons have been conducted by various researchers starting from 1950’s. A mixed-integer linear program was developed by Little (1966) for an arterial with number of signals in order to maximize the sum of the bandwidths for the two directions. Several variants of the problem were formulated, including the problem of synchronizing a network of signals. The solution of mixed-integer linear programs was arrived at by decrypting sequences of ordinary linear
Scope and objectives
To enable effective planning and functioning of signalized arterials, a better perception of platooning phenomenon is required. Hence the main motives for the present work is to understand the platooning phenomenon under heterogeneous traffic so that it can be used for designing better traffic signals under such conditions. It focuses essentially on the characteristics and interactions of vehicles of different categories under heterogeneous transport conditions, which will provide a basis for
Data collection and extraction
The section for collecting on-site traffic information was chosen considering the geometry of the road and the movement of traffic. An at-grade intersection located along a four lane divided urban road, devoid of side frictions and having uniform cross-section, along straight and level terrain is selected. An intersection in the city of Thiruvananthapuram in the southernmost State of Kerala in India, which satisfied the data collection requirements was selected as the study area. Traffic data
Measures to quantify speed variability
Platoon dispersion is the deterioration in the platoon compactness due to the variation in vehicle speeds. The magnitude of variation in speed reflects the level of interaction between the vehicles. The absence of lane discipline and presence of vehicles of various sizes and maneuverabilities observed under heterogeneous traffic stream cause vehicles to occupy any lateral position along the road width depending on the space availability. The quantification of variation in vehicle interactions
Pattern of platoon dispersion
The vehicles that leave a traffic signal as a dense platoon with small inter arrival times get gradually diffused as they progress along the downstream. Variation in acceleration rates and interactions during progression across downstream result in extension of platoon length, thus leading to initiation of platoon dispersion. Dispersion depends on the slope of the line represented in the time/distance graph. The dispersal of platoon is mainly due to the dissimilarity in the desired speeds of
Corroboration of the findings
The traffic data collected from study stretch 2 is used to validate the trend of platoon dispersion observed on the study stretch 1. The cycle time at the second intersection is 60 s which consists of a green phase of 24 s, a red phase of 33 s and an amber period of 3 s for the vehicle movement. The traffic volume observed in the study stretch varies from 15 veh/cycle (2250 veh per hour) to 32 veh/cycle (4800 veh per hour). The extraction of all the vehicle related data along the downstream
Conclusions
This study has determined the pattern of dispersion of platoons on the basis of measures such as profiles of speed, standard deviation, relative standard deviation, relative speed difference and platoon characterizing variables which quantify speed variability. The major findings from the study are as follows:
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The speed variability measures estimated for various categories of vehicles suggest that there is considerable variation in speed of progression of vehicles. But the pattern of dispersion
Acknowledgements
The authors acknowledge that this research work is supported by the Centre for Engineering Research and Development and the Transportation Engineering Research Centre, Government of Kerala, India.
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