Springer Tracts in Civil Engineering Marco Guerrieri Raffaele Mauro A Concise Introduction to Traffic Engineering Theoretical Fundamentals and Case Studies Springer Tracts in Civil Engineering Series Editors Giovanni Solari, Wind Engineering and Structural Dynamics Research Group, University of Genoa, Genova, Italy Sheng-Hong Chen, School of Water Resources and Hydropower Engineering, Wuhan University, Wuhan, China Marco di Prisco, Politecnico di Milano, Milano, Italy Ioannis Vayas, Institute of Steel Structures, National Technical University of Athens, Athens, Greece Springer Tracts in Civil Engineering (STCE) publishes the latest developments in Civil Engineering - quickly, informally and in top quality. 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The use of general descriptive names, registered names, trademarks, service marks, etc. in this publicationdoesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfrom therelevantprotectivelawsandregulationsandthereforefreeforgeneraluse. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained hereinorforanyerrorsoromissionsthatmayhavebeenmade.Thepublisherremainsneutralwithregard tojurisdictionalclaimsinpublishedmapsandinstitutionalaffiliations. ThisSpringerimprintispublishedbytheregisteredcompanySpringerNatureSwitzerlandAG Theregisteredcompanyaddressis:Gewerbestrasse11,6330Cham,Switzerland Preface This book contains a selection offundamentals topics of traffic engineering useful for highways facilities design and control. The treatment is basic, but it does not neglect to illustrate the most recent and crucial theoretical aspects which are at the root of several Highway Engineering applications, like, for instance, the essential aspects of highways traffic stream reliability calculation and automated highway systems control. In order for these topics to be better understood, varied illustrative examples of applicationsareprovidedingreatdetail.Wehaveactuallysoughttouseanintuitive and discursive, rather than formal and abstract style throughout the book. Shortly, the contents are as follows: (cid:129) Chapter 1 provides the definition of macroscopic traffic variables and the deduction of the fundamental traffic flow relationship; (cid:129) Chapter 2 offers an intuitive definition of transport demand, capacity and flow. The main macroscopic flow models, levels of service and traffic hysteresis phenomena are also dealt with; (cid:129) Chapter3gives anintroduction totheflowcontinuityequation, dynamictraffic flow models and kinematic and shock waves. Since these topics are usually difficult for beginners, the mathematical treatment is highly detailed; (cid:129) Chapter 4 describes some of the main microscopic models (linear and nonlin- ear).Thesedynamictrafficmodelsinvolvestudyinglocalinstability,asymptotic instability and flow breakdown. Moreover, a genealogy of the main traffic models (macroscopic, mesoscopic and microscopic) is reviewed in a synthetic way; (cid:129) Chapter 5 deals with the fundamentals of random and traffic processes and provides a very accurate description of probability models for arrival, speed, headwayandvehiculardensityprocesses.Alsothemaincounting,headwayand speed probability distributions are shown; (cid:129) Chapter 6 presents an advanced method for estimating flow reliability on highwaysanddescribesthecurrentsystemsofhighwaytrafficmanagementand control. In this chapter, a rigorous capacity definition is offered. The basic v vi Preface characteristics of the Automated Highway System are also introduced. Finally, theHSMmethodtoestimate theannual crash frequencyexpectedonhighways and the COPERT method to calculate the polluting emissions are both illustrated; (cid:129) Chapter 7 presents the gap acceptance theory, in that it is of great applicative interest in studying road intersections. Therefore, some models for estimating the critical gap and the follow-up time for at-grade unsignalized intersections and roundabouts are described; (cid:129) Chapter 8 deals with the models for studying queues in road transport systems underaunitaryapproach.Theyaretheprobabilisticmodelsforstationarystate, the deterministic solutions in congestion, and the heuristic solutions for sta- tionary and non-stationary states. The treatment of these models is unusual but can be directly applied to practical cases; (cid:129) Chapter9dealswithunsignalizedintersectionsandmethodsfordeterminingthe measures of effectiveness (MOE): waiting times and delays. To this regard, the TRLmethodforestimatingcapacity,queues,delaysatthree-armintersectionsis exemplified; (cid:129) Chapter10covers signalizedintersections.TheHCM modelforthecalculation and functional analysis of such intersections is illustrated in detail. AndreaPompigna,Ph.D.inTransportationEngineering,istheauthorofChap.8. We are deeply grateful to Andrea Pompigna also for his invaluable help in dis- cussing critically the topics with us, as well as revising the whole book in a systematic way. Finally, we wish to thank Autostrade del Brennero S.p.A. (Trento) for sup- portingourrecentresearchontrafficflowtheoryandcontrolatDICAM,University of Trento. Palermo, Italy Marco Guerrieri Palma Campania (Naples), Italy Raffaele Mauro July 2020 Contents 1 MacroscopicVariablesandFundamentalRelationshipsofTraffic Flow Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 Interrupted and Uninterrupted Traffic Flows . . . . . . . . . . . . . . . 1 1.2 Inference of Macroscopic Flow Variables. . . . . . . . . . . . . . . . . 2 1.2.1 Traffic Variables Referred to the Time Domain . . . . . . 4 1.2.2 Traffic Flow, Traffic Volume and Capacity . . . . . . . . . 8 1.2.3 Peak Hour Factor. . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.2.4 Estimating of Design Hourly Volume DHV. . . . . . . . . 11 1.2.5 Traffic Variables Referred to the Space Domain. . . . . . 13 1.2.6 Fundamental Flow Relationship . . . . . . . . . . . . . . . . . 16 1.2.7 Traffic Flow Stationarity. . . . . . . . . . . . . . . . . . . . . . . 18 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2 Macroscopic Traffic Flow Models . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.1 Transportation Demand, Capacity and Flow . . . . . . . . . . . . . . . 23 2.2 Relationship Between Macroscopic Traffic Flow Variables . . . . 26 2.3 Properties of the Mathematic Traffic Flow Models and Operational Flow Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.3.1 Single-Regime Models . . . . . . . . . . . . . . . . . . . . . . . . 29 2.3.2 Levels of Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.3.3 Other Characterizations of the Operational Traffic Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 2.4 Experimental Definition of a Traffic Flow Model . . . . . . . . . . . 35 2.5 Deterministic Multi-regime Traffic Flow Models. . . . . . . . . . . . 36 2.6 Physical Interpretation of the Capacity. . . . . . . . . . . . . . . . . . . 36 2.7 Hysteresis in Traffic Flows . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.8 Kerner’s Three-Phase Traffic Theory . . . . . . . . . . . . . . . . . . . . 38 2.9 Case Study: Service Levels According to Greenshields’ Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 vii viii Contents 2.10 Case Study: Calibration of Greenshields’ Flow Model . . . . . . . 41 2.11 Case Study: Calibration of May’s Flow Model. . . . . . . . . . . . . 44 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 3 Continuity Flow Equation, Kinematic Waves and Shock Waves. . . 49 3.1 Fluid Dynamic Analogy for the Traffic Flow . . . . . . . . . . . . . . 49 3.1.1 Deduction of the Continuity Equation . . . . . . . . . . . . . 51 3.1.2 Boundary and Initial Conditions . . . . . . . . . . . . . . . . . 52 3.1.3 Kinematic Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 3.1.4 Perturbations of the Traffic Flow and Speed. . . . . . . . . 57 3.2 The LWR Model and Shock Waves. . . . . . . . . . . . . . . . . . . . . 58 3.2.1 Case Study: Queue Formation and Dissipation Due to Presence of a Heavy Vehicle on a Two-Lane Undivided Highway . . . . . . . . . . . . . . . . . . . . . . . . . . 62 3.2.2 Case Study: Estimation of the Effects of an Accident on the Flow in a Two-Lane Dual Carriageway Highway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 4 Microscopic Models and Traffic Instability. . . . . . . . . . . . . . . . . . . 65 4.1 Microscopic Models: Car-Following Theory. . . . . . . . . . . . . . . 65 4.2 Linear Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 4.3 Impulsive Variations of Vehicle Speeds: Traffic Instability and Stop (‘phantom Traffic Jams’). . . . . . . . . . . . . . . . . . . . . . 67 4.3.1 Local Instability and Asymptotic Instability . . . . . . . . . 72 4.4 Non-linear Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 4.5 Derivation of Macroscopic Models from the Microscopic Non-linear Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 4.6 Traffic Model Genealogy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 5 Fundamentals of Random and Traffic Processes. . . . . . . . . . . . . . . 77 5.1 Traffic Processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 5.2 Counting Probability Distributions. . . . . . . . . . . . . . . . . . . . . . 84 5.2.1 General Criterion for Selecting the Appropriate Counting Probability Distribution . . . . . . . . . . . . . . . . 86 5.3 Probability Distribution for Time Headways. . . . . . . . . . . . . . . 94 5.4 Speed Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6 Traffic Management and Control Systems . . . . . . . . . . . . . . . . . . . 103 6.1 Preliminary Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 6.2 Flow Reliability on Highways . . . . . . . . . . . . . . . . . . . . . . . . . 104 6.2.1 Case Study: Assessment of the Reliability Laws from Traffic Surveys. . . . . . . . . . . . . . . . . . . . . . . . . . 106 Contents ix 6.3 The Ramp-Metering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 6.3.1 System Analysis for an Isolated On-Ramp. . . . . . . . . . 109 6.3.2 System Analysis for On-Ramps and Off-Ramps . . . . . . 111 6.4 Hard Shoulder Running System. . . . . . . . . . . . . . . . . . . . . . . . 113 6.4.1 Capacity Estimation of Highways with HSR System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 6.4.2 Case Study: Traffic Flow Parameters Estimation After HSR System Activation . . . . . . . . . . . . . . . . . . . 114 6.5 Variable Speed Limits (VSL) . . . . . . . . . . . . . . . . . . . . . . . . . 116 6.6 Automated Highway System (AHS). . . . . . . . . . . . . . . . . . . . . 118 6.6.1 Estimation of the Increase in Lane Capacity. . . . . . . . . 119 6.7 C-ITS, C-Roads and Smart-Roads . . . . . . . . . . . . . . . . . . . . . . 120 6.7.1 C-ITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 6.7.2 C-Road Platform . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 6.7.3 Smart-Roads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 6.8 Crash Frequency Estimation: The HSM Method. . . . . . . . . . . . 123 6.9 Models for Estimating Traffic Pollutant Emissions . . . . . . . . . . 125 6.9.1 The Macroscopic Model COPERT . . . . . . . . . . . . . . . 125 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 7 Interference Between Traffic Flows: The Gap Acceptance Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 7.1 Estimation of the Critical Gap and Follow-Up Time . . . . . . . . . 133 7.1.1 Estimation of the Average Critical Gap: Ashworth’s Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 7.1.2 Estimation of the Average Critical Gap: Miller’s Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 7.2 Characteristic Values of the Critical Gap and the Follow-Up Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 7.2.1 T and T for Unsignalized Intersections . . . . . . . . . . . 135 c f 7.2.2 T and T for Roundabouts . . . . . . . . . . . . . . . . . . . . . 136 c f 7.3 TheTheoreticalCapacityofTrafficStreamsinanUnsignalized At-Grade Intersection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 8 Queue Formation: General Models. . . . . . . . . . . . . . . . . . . . . . . . . 141 8.1 Queuing Systems: Variables and Basic Relationships . . . . . . . . 142 8.1.1 Little’s Law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 8.2 Operating Conditions and Models for Waiting Systems. . . . . . . 146 8.3 Probabilistic Models for Steady-State. . . . . . . . . . . . . . . . . . . . 147 8.4 Deterministic Solutions in Congestion . . . . . . . . . . . . . . . . . . . 152 8.5 Heuristic Solutions for Steady and Non-steady States . . . . . . . . 155 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161