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Speed–density functional relationship for heterogeneous traffic data: a statistical and theoretical investigation

Journal of Modern Transportation 2019年第1期27卷 61-74页

作者： hari krishna gaddam K.Ramachandra Rao Department of Civil Engineering Indian Institute of Technology

This study is an attempt to establish a suitable speed–density functional relationship for heterogeneous traffic on urban arterials. The model must reproduce the traffic behaviour on traffic stream and satisfy all static and dynamic properties of speed–flow–density relationships. As a first attempt for Indian traffic condition, two behavioural parameters, namely the kinematic wave speed at jam(Cj) and a proposed saturation flow(k), are estimated using empirical observations. The parameter Cjis estimated by developing a relationship between driver reaction time and vehicle position in the queue at the signalised intersection. Functional parameters are estimated using Levenberg–Marquardt algorithm implemented in the R statistical *** measures such as root mean squared error, average relative error and cumulative residual plots are used for assessing models fitness. We set out several static and dynamic properties of the flow–speed–density relationships to evaluate the models, and these properties equally hold good for both homogenous and heterogeneous traffic *** the numerical analysis, it is found that very few models replicate empirical speed–density data traffic ***, none of the existing functional forms satisfy all the properties. To overcome the shortcomings, we proposed two new speed–density functional forms. The uniqueness of these models is that they satisfy both numerical accuracy and the properties of fundamental diagram. These new forms would certainly improve the modelling accuracy, especially in dynamic traffic studies when coupling with dynamic speed equations.

关键词： Heterogeneous traffic Speed-density model Kinematic wave speed Traffic flow CURE plots

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Comparative evaluation of roundabout capacities under heterogeneous traffic conditions

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Journal of Modern Transportation 2015年第4期23卷 310-324页

作者： Ramu Arroju hari krishna gaddam Lakshmi Devi Vanumu K.Ramachandra Rao Department of Civil Engineering IIT Delhi Department of Civil Engineering and Transportation Research and Injury Prevention Programme (TRIPP) IIT Delhi

In heterogeneous traffic conditions, roundabout capacity is described by vehicle and driver characteristics which are different from traffic conditions in homogeneous conditions. In the present study, the capacity of the roundabout is determined using various capacity formulas such as gap acceptance models given by Highway Capacity Manual 2010 （US）, German model （2001）; empirical regression models given by TRRL （UK） and weaving models given by IRC： 65-1976 （India）. In addition, microscopic simulation model like VISSIM （PTV Ger- many） is also used to derive capacity values. Unlike the other capacity estimation models, VISSIM is helpful in estimating capacity values using geometric and driver characteristics and it can also simulate heterogeneous traffic condition accurately. Capacity is estimated after calibrating the simulation model （VISSIM） developed for the roundabout. This is achieved by incorporating different vehicle classes to represent the heterogeneous traffic environment, driver gap acceptance, and lane changeparameters. All the required inputs were extracted from the video using semi-automatic data collection methods. Data are used for the estimation of capacity values from dif- ferent methods mentioned above and for the calibration and validation of simulation model. The capacity values esti- mated form various formulas except German model are distinctly different from the field values and they are either overestimating or underestimating. Analysis of these observations reveals that the capacity values from VISSIM and German models are nearly matching with the field capacity.

关键词： Roundabout Capacity VISSIM Simulation Heterogeneous

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