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Traffic Management

Cover of Guide to Traffic Management Part 2: Traffic Theory Concepts
Guide to Traffic Management Part 2: Traffic Theory Concepts
  • Publication no: AGTM02-26
  • ISBN: 978-1-923617-20-9
  • Published: 28 January 2026
  • Edition: 4.0

Guide to Traffic Management Part 2: Traffic Theory Concepts provides practitioners with the theoretical background necessary to appreciate the nature of traffic behaviour and to undertake analyses required in the development and assessment of both traffic management plans and road design proposals.

Fundamentals of Traffic Management: Online Training

These freely available online learning units cover the fundamentals of traffic management. The units cover 22 modules, each includes a video with in-session exercises.

The modules related to Guide to Traffic Management Part 2 are:

In this edition, the information about gap acceptance (Section 5.1.1) has been updated and a new Section 5.1.3 Measuring Gap Acceptance Parameters has been added. The Guide has also been updated to:

  • improve the documentation of gap acceptance analyses
  • use the Cowan (1975) headway distribution
  • update references to the 7th edition of the Highway Capacity Manual.

Superseded editions:

Edition 3.0 published April 2020

Edition 2.0 published October 2015

Edition 1.0 published July 2008

  • 1. Introduction
    • 1.1 Purpose
    • 1.2 Intended User
    • 1.3 How to Use
    • 1.4 Scope
    • 1.5 Out of Scope
  • 2. Basic Traffic Variables and Relationships
    • 2.1 Basic Descriptors of Traffic Flow
      • 2.1.1 Volume
      • 2.1.2 Density
      • 2.1.3 Speed
      • 2.1.4 Headway
      • 2.1.5 Spacing
      • 2.1.6 Gap
      • 2.1.7 Lane Occupancy
    • 2.2 Mathematical Relationships
      • 2.2.1 Fundamental Relationships
    • 2.3 Time and Space Mean Speed Relationships
    • 2.4 Graphical Relationships for Uninterrupted Flow
    • 2.5 Kinematic Wave Model
  • 3. The Stochastic Nature of Traffic Behaviour
    • 3.1 Probabilistic Aspects of Traffic Flow
    • 3.2 Statistical Distributions in Traffic
      • 3.2.1 The Binomial Distribution
      • 3.2.2 The Poisson Distribution
      • 3.2.3 Negative Binomial Distribution
      • 3.2.4 Geometric Distribution
      • 3.2.5 Negative Exponential Distribution
      • 3.2.6 Other Distributions
    • 3.3 Traffic Headway Distributions
      • 3.3.1 Random Arrivals – Negative Exponential Headways
      • 3.3.2 Equal Headways
      • 3.3.3 The Displaced Negative Exponential Distribution
      • 3.3.4 Cowan M3 distribution
      • 3.3.5 Other Headway and Platoon Length Distributions
      • 3.3.6 Matching Headway Distribution Type to Observed Behaviour
  • 4. Queuing
    • 4.1 Introduction and Definitions
    • 4.2 Graphical Representation of Queues
    • 4.3 Dynamic and Steady State Queuing
    • 4.4 Steady State Queues with Random Arrivals and Service
      • 4.4.1 Queue Lengths
      • 4.4.2 Waiting Times in Queues
    • 4.5 Example Application of Steady State Queuing Theory
    • 4.6 Summary of Queuing Theory Formulae
  • 5. Gap Acceptance
    • 5.1 Introduction and Definitions
      • 5.1.1 General Introduction
      • 5.1.2 Definitions
      • 5.1.3 Measuring Gap Acceptance Parameters
    • 5.2 Principal Gap Acceptance Formulae
      • 5.2.1 Delays
      • 5.2.2 Absorption Capacities
      • 5.2.3 Multi-lane Flows
    • 5.3 More Complex Gap Acceptance Situations
      • 5.3.1 Minor Road Approaches with Mixed Traffic
      • 5.3.2 Different Critical Gaps for Different Conflicting Major Flows
    • 5.4 Formulae for Cowan M3 Headways in the Major Traffic Stream
    • 5.5 Estimating Total Delays
      • 5.5.1 Estimating Delays to Vehicular Traffic
      • 5.5.2 Estimating delays to pedestrians and cyclists
    • 5.6 Example Applications of Gap Acceptance Analysis
      • 5.6.1 Example 1 – Random Arrivals on Major Road, Mixed Minor Road Traffic
      • 5.6.2 Example 2 – Displaced Negative Exponential Headways on Major Road
      • 5.6.3 Example 3 – Staged Crossing
      • 5.6.4 Example 4 – Estimating the Critical Gap from Field Data
    • 5.7 Summary of Basic Gap Acceptance Formulae
  • 6. Combined Gap Acceptance and Queueing Theory
    • 6.1 Absorption Capacity as a Queuing Service Rate
    • 6.2 Gap Acceptance with Multiple Levels of Priority
  • 7. Vehicle Interactions in Moving Traffic
    • 7.1 Overview
    • 7.2 Car Following
      • 7.2.1 Pipes’ Model
      • 7.2.2 Forbes’ Model
      • 7.2.3 General Motors’ Models
    • 7.3 Traffic Bunches and Overtaking
      • 7.3.1 General
      • 7.3.2 Traffic Bunches
      • 7.3.3 Overtaking on Two-lane, Two-way Roads
      • 7.3.4 Bunching and Overtaking as Level of Service Measures
    • 7.4 Platoon Dispersion
      • 7.4.1 General
      • 7.4.2 Kinematic Wave Theory
      • 7.4.3 Diffusion Theory
      • 7.4.4 Recurrence Model
    • 7.5 Congestion Management Theory
      • 7.5.1 General
      • 7.5.2 Flow Monitoring and Management
      • 7.5.3 Two Phase HCM Model
      • 7.5.4 Three Phase Model
      • 7.5.5 Other Models of Flow Breakdowns
  • 8. Principles Underlying Managed Motorways
    • 8.1 Causes and Impacts of Flow Breakdowns
      • 8.1.1 Bottlenecks
      • 8.1.2 Non-recurrent Causes of Flow Breakdown
      • 8.1.3 Effects of Flow Breakdown
      • 8.1.4 Recovery from Flow Breakdown
    • 8.2 Motorway Operational Capacity
      • 8.2.1 Capacity of Segment
      • 8.2.2 Capacity at Motorway Entry Ramp Merges
    • 8.3 Merge Capacity for a Managed Motorway with Ramp Signals
    • 8.4 Theory Underlying Variable Speed Limits (VSL)
  • References
  • Commentary 1
    • C1.1 Space Mean Speed and Time Mean Speed
  • Commentary 2
    • C2.1 Implications of a Perfect Linear Speed-Density Relationship
  • Commentary 3
    • C3.1 Derivations of Queue Length Formulae in Section 4.4.1
  • Commentary 4
    • C4.1 Derivations of Queue Delay Formulae in Section 4.4.2
  • Commentary 5
    • C5.1 Derivations of Formulae in Section 5.2.1 for Delays to Minor Traffic in Gap Acceptance Situations
  • Commentary 6
  • Commentary 7
    • C7.1 Average Delay
  • Commentary 8
    • C8.1 Derivation of Theoretical Absorption Capacity Formula in Section 5.2.2
  • Commentary 9
  • Commentary 10
    • C10.1 Derivation of Gap Acceptance Formulae for Cowan M3 Distribution of Headways in the Major Traffic Flow
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