Investigation Of Traffic Capacity For A Roundabout

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

ACKNOWLEDGEMENT

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 ORGANIZATION

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.