Description
ABSTRACT
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, German model (2001); empirical regression models given by TRRL and weaving models given by IRC: 65–1976 . In addition, microscopic simulation model like VISSIM (PTV Germany) 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 change parameters. 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 different methods mentioned above and for the calibration and validation of simulation model. The capacity values estimated 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.
TABLE OF CONTENTS
COVER PAGE
TITLE PAGE
APPROVAL PAGE
DEDICATION
ACKNOWELDGEMENT
ABSTRACT
CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
- PROBLEM STATEMENT
- AIM OF THE STUDY
- PURPOSE OF THE STUDY
- SIGNIFICANCE OF THE STUDY
- SCOPE OF THE STUDY
- PROJECT ORGANISATION
CHAPTER TWO
LITERATURE REVIEW
- REVIEW OF THE STUDY
- OVERVIEW OF ROUNDABOUT
- HISTORICAL BACKGROUND OF ROUNDABOUT
- HISTORICAL BACKGROUND OF ROUNDABOUT
- OPERATION AND DESIGN OF MODERN ROUNDABOUTS
- TYPES OF CIRCULAR INTERSECTIONS
- CAPACITY ESTIMATION
CHAPTER THREE
3.0 METHODOLOGY
- INTRODUCTION
- DATA COLLECTION
- CALIBRATION
- VALIDATION
CHAPTER FOUR
4.0 RESULTS AND ANALYSIS
- CRITICAL HEADWAY ESTIMATION
- FOLLOW-UP HEADWAY
- HCM 2010 METHOD
- TRRL (UK) LINEAR REGRESSION METHOD
- THE ROADS CONGRESS METHOD (IRC 65-1976)
- GERMAN METHOD
- ENTRY FLOW VERSUS CIRCULATING FLOW CURVES
- FLOW VERSUS DENSITY CURVES
CHAPTER FIVE
- CONCLUSION
- RECOMMENDATION
- REFERENCES
CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Roundabouts have many advantages compared to other regular signalized intersections. The main advantages are traffic safety, operational performance, environmental factors, pedestrian safety, and aesthetics [1]. Signalized intersection has 32 conflict points whereas roundabout with one circulating lane and one entry lane has 8 traffic conflict points. But the number of conflicts increases to 16 in the case of roundabout with two circulating and two entry lanes. Conflict points at signalized intersection and roundabout with one circulating and one entry lane are depicted in Figs. 1 and 2, respectively. The reduced number of conflict points at a roundabout indicates the reduction of crash propensity. The increased use of roundabout as a traffic facility needs an overall assessment on potential accident rates [2]. For the safe movement of the vehicles, it is essential to understand the operational performance of the roundabout. Capacity is one such parameter which explains the operational performance, traffic scenario, and level of service.
Fig. 1 Conflict points at signalized intersections
Fig. 2 Conflict points at a single-lane Roundabout
In contrast to traffic flow condition in developed countries, Indian traffic condition is totally different. Apart from the different driver classes, vehicles with various performance and dimensional characteristics (especially traffic is predominantly occupied by small sized vehicles such as motor two wheelers and auto rickshaws), non-lane discipline, and creeping behavior are characterized a totally complex traffic environment. It requires special attention in modeling traffic flow behavior. Several capacity formulas under steady-state conditions are developed for various countries such as Highway Capacity Manual (HCM) method for US [3], TRRL method for UK [3], German method [3], and IRC method for India [4]. However, these are very limited in terms of being able to reproduce the actual traffic conditions prevalent and also they do not have many calibration parameters to improve the estimates. VISSIM microscopic simulation helps in addressing this aspect. Besides, it has several calibration parameters which can also help improve the accuracy of the capacity estimates. The heterogeneous traffic can be introduced by importing various vehicle 3D models which are not in VISSIM by default like Auto, etc. It can incorporate both geometry of the roundabout and driver gap acceptance behavior and hence is the most accurate to estimate capacity compared to all the methods available. So, in this study, the first objective is to calibrate and validate the VISSIM model for heterogeneous traffic situation. Few Methods have been developed to estimate empirical capacity values using different approaches [5, 6], and comparative analysis of the several models can also be done using flows and delays [7]. As a second objective, in the present study, we adopted a new approach to estimate empirical capacity values to compare the performance of various methods in estimating capacity values.
1.2 PROBLEM STATEMENT
Before now, many clashes occur in roundabout as a result of inability of the roundabout to contain the number of vehicle that approaches it and the driver ignorance of the capacity of the roundabout. This study came to address this issue. It is used to determine the capacity of a roundabout thereby providing more efficient traffic flow.
1.3 AIM OF THE STUDY
The main aim of this work is to investigate roundabout capacity analysis using different formulas and models. In this work, the capacity of the roundabout is determined using various capacity formulas such as gap acceptance models given by Highway Capacity Manual, German model (2001); empirical regression models given by TRRL and weaving models given by IRC: 65–1976 . In addition, microscopic simulation model like VISSIM (PTV Germany) is also used to derive capacity values.
1.4 PURPOSE OF THE STUDY
Roundabouts are one of the most environmentally sustainable infrastructure design strategies to significantly reduce greenhouse gas emission [1–3]. The goal of sustainable infrastructure is to protect the environment and conserve resources while taking into consideration intended needs as well as benefits and costs. Roundabouts, compared with other intersection applications including traffic signals and all-way stop control, can accomplish sustainability purposes by eliminating power needs and making more efficient traffic flow.
1.5 SCOPE OF THE STUDY
The capacity in approach section in roundabout is calculated by estimating the number of vehicles that can enter a roundabout for a given approach given a certain circulating volume. Since roundabouts are working with only yield conditions, capacity is dependent on gap acceptance model. Priority rules are used to simulate the gap acceptance model and define the right-of-way for conflicting movements. In the case of roundabouts, priority rules can be utilized to establish right-of-way at each of the conflict points where the approach traffic merges with the circulating traffic of the roundabout.
1.6 SIGNIFICANCE OF THE STUDY
This study is used to determine the maximum number of vehicles that can enter a roundabout for a given approach given a certain circulating volume. Since roundabouts are un-signalized with only yield conditions, capacity is dependent on gap seeking logic. If a vehicle has an acceptable gap in circulating flow, the vehicle will proceed to enter the roundabout, else it must wait until an acceptable gap is available. In microscopic traffic simulation model VISSIM, the priority rule is used to simulate the gap seeking logic. By altering the minimum acceptable gap (with additional parameters no discussed herein), it is possible to calibrate a simulation model to be that of a real-life roundabout or that of a theoretical roundabout that meets the operating characteristics of the Highway Capacity Manual.
1.7 PROJECT ORGANISATION
The remaining portion of the paper is structured as follows. The second section explains about capacity estimation methods. The third section tells about the methodology adopted for this study, data collection procedure, calibration, and validation. The fourth section illustrates the capacity values estimated from various methods and comparison of capacity values. The fifth is about the conclusions.
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