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EFFECTS OF VEHICLE TYPE ON HIGHWAY TRAFFIC FLOW Effects of vehicle type on speed, delay and capacity characteristics of highway traffic flow in the United Kingdom and Saudi Arabia determined by an examination of traffic data A Thesis presented for the degree of DOCTOR OF PHILOSOPHY of the UNIVERSITY OF BRADFORD in the POSTGRADUATE SCHOOL OF STUDIES IN CIVIL AND STRUCTURAL ENGINEERING ALI AL-AKHDAR CALKAIM January 1987 BEST COPY AVAILABLE Variable print quality CONTENTS Acknowledgements Abstract CHAPTER I : INTRODUCTION 1.1 Vehicle Features 1.1.1 Size 1.1.2 Weight 1.1.3 Types (Classifications) 1.2 Effect of Vehicle Type on Highway Design 1.2.1 Lane Width 1.2.2 Turning Circles at Junctions 1.3 Effect of Vehicle Type on Capacity 1.3.1 Between Intersection Situations 1.3.2 At Priority Junctions 1.3.3 At Roundabouts 1.3.4 At Signalized Intersections 1.3.5 At Grade Separated Intersections 1.4 Effect of Vehicle Type on Delay 1.4.1 Introduction 1.4.2 At Signalized Intersections 1.4.3 At Priority Intersections 1.4.4 At Roundabouts CHAPTER I1 : EFFECTS OF VEHICLE TYPE AT TRAFFIC SIGNALS 78 2.1 Introduction 78 Contents cont . Page 2.2 Spacing and Headway Characteristics 83 2.3 Saturation Flow Criteria 2.3.1 Definitions and Notation 2.3.2 Effective Green Time 2.3.3 Approach Width and Saturation Flow Relationship 2.3.4 Methods of Estimation of Saturation Flow 2.4 Current Approach to the Use of Passenger Car Units 2.4.1 Definition 2.4.2 Methods of Calculating PCU1s 2.5 Site Selection and Description 2.5.1 Introduction 2.5.2 Site Selection Criteria 2.5.3 , Site Descriptions 2.6 Method of Observation 2.6.1 Introduction 2.6.2 Filming Technique and Data Collection 2.6.3 The Method Adopted for Data Collection 2.6.4 Film Analysis 2.7 Data Analysis 2.7.1 Vehicle Type Definition 2.7.2 Theoretical Basis of the Analysis 2.7.3 Computer Programming and Analysis 2.8 Presentation of Results, 2.8.1 Introduction 2.8.2 Saturation Flows and Lost Time 2.8.3 Passenger Car Unit Values Contents cont. Page 2.9 Comparison of Results with Existing Values 189 2.9.1 Saturation flows 189 2.9.2 Mixed Turning Movement Lanes 191 2.9.3 A Comparison of Computed and Existing 195 Passenger Car Unit Values 2.10 Vehicle Type Delay Relationship 204 CHAPTER I11 : EFFECT OF VEHICLE TYPE AT ROUNDABOUT 220 ENTRIES 3.1 Introduction 220 3.2 Historical Review 222 3.2.1 Roundabout Intersections 222 3.2.2 The Priority Rule 225 3.3 Roundabout Traffic Parameters 3.3.1 Traffic Capacity 3.3.2 Gap Acceptance Studies 3.3.3 Delay Criteria 3.4 An Analysis of Vehicle Type Effects on Junction 240 Performance 3.4.1 Vehicle Type and Circulating Flow 240 3.4.2 Vehicle Type and Roundabout Performance 242 3.5 Site Selection and Description 244 3.5.1 Introduction 244 3.5.2 Site Selection Criteria 245 3.5.3 Site Descriptions 3.6 Filming Techniques and Data Collection Contents cont. Page 3.7 Gap Acceptance Observation Analysis and Distri- bution fitting 3.7.1 Vehicle Type Gap Acceptance Distributions 3.7.2 Gap Accepted Range and Vehicle Type Re1.a- tionship 3.8 Passenger Car Unit Analysis 3.8.1 Procedure Adopted for Computing Passenger Car Units 3.8.2 Computer Programming and Analysis 3.8.3 Passenger Car Units in Urban Situations 3.8.4 Passenger Car Units in Semi-Rural Situa- tions 3.9 The Effect of Vehicle Type on Entry Capacity 3.9.1 Introduction 3.9.2 Vehicle Type Entry/Circulating Flow Rela- tionship 3.9.3 Comparison with TRRL Unified Capacity Formula 3.10 Effect of Vehicle Type on Delay CHAPTER IV : EFFECT OF VEHICLE TYPE ON RURAL MOTORWAY FLOW 4.1 Introduction and Summary 4.2 Speed Distribution Studies 4.2.1 Introduction 4.2.2 Speed-Flow variation by Hour of Day 4.2.3 Speed- low elation ship for Multilane Highways Contents cont. Page 4.2.4 Speed-Flow Relationship for Two-Lane 358 Highways 4.3 Capacity Studies 4.3.1 Introduction 4.3.2 Two-Lane Capacity Prediction 4.4 Level of Services 4.5 Theory and Study Approach 4.5.1 Introduction 4.5.2 Vehicle Type Speed Studies 4.5.3 Procedure for Computing Passenger Car Unit Equivalencies 4.5.4 An Analysis of Vehicle Type Effects on 389 Highway Traffic Parameters 4.6 Site Selection and Description 390 4.7 Method of Observation 395 4.7.1 Filming Technique and Data Collection 395 4.7.2 The Method Adopted for Film Analysis 399 4.8 Speed Observations Analysis 4 03 4.8.1 Vehicle Type Speed Distribution 403 4.8.2 ~ittingNormal Distributions 404 4.9 Vehicle Type Distribution 445 4.10 Passenger Car Unit Equivalencies Values for Two- 451 Lane Rural Highways 4.10.1 Vehicle Type Overtaking Criteria 451 4.10.2 Vehicle Types Equivalents 453 Contents cont . Page 4.11 An Analysis of Vehicle Type Effect on Highway 475 Traffic Parameters 4.11.1 Effect of Vehicle Type on Speed/Flow 475 Capacity Relationships 4.11.2 Overtaking Procedure and Vehicle Type 486 Effects CHAPTER V : EFFECTS OF VEHICLE TYPE AND TRAFFIC GROWTH ON TRAFFIC PERFORMANCE IN SAUDI ARABIA 5.1 ~ntroduction 500 5.2 Development of the Road Network 504 5.2.1 ~ntroduction 504 5.2.2 Urban Road 508 5.2.3 Rural Roads 516 5.3 Traffic Growth 526 5.4 Effects of Vehicle Type 530 5.4.1 Vehicle Type 530 5.4.2 The Effect of Vehicle Type on Road 534 Network Design 5.4.3 The Effect of Vehicle Type on Urban Traffic537 5.5 Traffic Standards and Specifications 544 5.5.1 Traffic Signals 544 5.5.2 Signal Controlled Junction Design 547 5.6 Passenger Car Unit Values at Signalized 554 Intersections Contents cont. Page List of References Appendices ACKNOWLEDGEMENTS The author wishes to express his sincere gratitude to Dr. R. J. Salter, Chairman of Postgraduate School of Studies in Civil and Structural Engineering, for his counsel, encouragement and guidance during the course of this research. He also wishes to express his appreciation for the conscientious and hard work done by Mrs. M. A. Manasir, in so intelligently and diligently typing this thesis. ABSTRACT The thesis considers the effects of vehicle type on highway traffic flow. The effects of vehicle type on the capacity of traffic signal approaches are examined by the experimental determination of passenger car units at intersections in London and West Yorkshire and in addition saturation flows and lost times are ex- amined. Vehicle type effects at roundabout entries are investigated and the results of field observations reported. Details are given of the gap acceptance of varying vehicle types, the effect of vehicle type on delay and comparisons are made with existing recommenda- tions for the capacity design of roundabout entries. Observations of traffic flow on a rural motorway are used to demonstrate the effect of vehicle type on speed and observed values are fitted to a normal distribution. Overtaking behaviour is also examined and conclusions drawn of the relative effect on capacity of vehicle type. A review is given of the effects of vehicle type on the design and operation of the highway system in Saudi Arabia. Introduction CHAPTER ONE Introduction 1.1 - Vehicle features 1.1.1 - Size The problem of the basic philosophy of vehicle size was initially recognized as early as 1920 in order to solve the productivity problem. Any in- crease in the allowable vehicle size would bring with it some gains in the economical use of highway transport, but this may cause highway deterioration, wider and higher load-rated bridges, decreasing visibility to other road users, to some extent diminishing trucks' operational ability as well as providing an economic advantage over other modes of transportation. Truck width, height and length exert an in- fluence on freight-loading practices, terminal facili- ties and the inter-city operation. They affect pave- ment and shoulder width, overhead clearance of structures, traffic safety and the movement of passenger cars. So the dimensional and performance characteri- stics of vehicles are basic to the regulation of road use and to the design of routes and terminals. In the traffic stream of today, there are three main categories of vehicles, private passenger cars, light and heavy goods vehicles and buses. In each category there is a wide range of makes and types of different performances. Different percentages of these categories present in the traffic stream necessi- tate the adoption of a suitable design standard. Highway design, quality of traffic movement, and both vehicle and roadway cost are affected directly by the dimensional aspects of vehicles. Pavement thickness, lane width, terminal layout, sight distance, and vertical clearance are some of the design features affected by the dimensional characteristics of vehicles. Also they influence the vehicle operating costs because of the fashion in which certain resistance forces (air, rolling inertia, etc.) are related to the vehicle design (e.g. fronted area). However, width of vehicle naturally affects the width of traffic lane, length has a bearing on roadway capacity and affects the turning radius and height of vehicle affects clearance of the various structures.