Transportation Planning

Bastian J. Schroeder, PhD, PE,    Director of Highway Systems, Institute for Transportation Research and Education (ITRE)

This part describes the basic process of planning and forecasting traffic demands and future conditions of the transportation system. Many planning applications are closely tied to new developments on a local or regional scale that are expected to impact traffic patterns. Transportation professionals use these planning methods to forecast how much traffic is expected in future-year analyses, where that traffic is expected to go, what routes that traffic is expected to take, and what modes of transportation travelers are most likely to choose. These methods aim to predict and estimate how drivers, the human element in any transportation problem, are likely to behave and act based on prior observations and historic trends. The text presents critical planning concepts and terms, and then introduces the reader to the four-step forecasting process used in transportation planning. The discussion includes data needs and sources for planning analyses, as well as mathematical models used to complete various steps in the forecasting process. The part concludes with a discussion of planning applications and software use, as well as practice problems to further explore and apply the concepts presented in the text.

Keywords

Transportation planning; Four-step process; Traffic impact analysis; Trip generation; Trip distribution; Mode choice; Traffic assignment; Travel demand modeling

Contents

2.1 Introduction 19

2.1.1 Purpose of Transportation Planning 19

Metropolitan Planning Organization 21

State Department of Transportation Planning Organization 23

Regional Transportation Planning Organization 23

Prioritizing Transportation Investments 24

Emphasizing Agency Coordination 25

Planning Applications and Topics 26

2.1.2 Accuracy and Error in Forecasting 27

2.2 Planning Concepts and Four-Step Process Overview 27

2.2.1 Regional and Statewide Planning Process 27

2.2.2 Traffic Impact Analyses 30

Scope 31

Process 32

Typical Mitigation Strategies 33

2.2.3 Highway Functional Classification System 34

2.2.4 Planning Data and Data Sources 37

Traffic Counts 38

Average Daily Traffic 39

Design Hourly Volume and Directional Design Hourly Volume 40

Peak Hour Volume 43

2.3.1 Planning Definitions and Terms 45

2.3 Trip Generation 49

2.3.1 Land Use Types 50

2.3.2 Estimating Generated Trips 51

2.4.1 Sample Network Application of Trip Generation 54

2.4 Trip Distribution 54

2.4.1 Gravity Model 56

2.4.2 Use of Data and Calibration 58

2.4.3 Sample Network Application of Trip Distribution 60

2.5 Mode Choice 64

2.5.1 Trip End Models 64

2.5.2 Trip Interchange Models 65

Variables Impacting Mode Choice 66

Utility Models 67

Types of Logit Models 69

2.6 Traffic Assignment 70

2.6.1 Network, Paths, and Skimming 70

2.6.2 Shortest Path Assignment 73

2.7.1 Capacity-Constrained Assignment 77

2.7.2 Dynamic Traffic Assignment and Other Advanced Algorithms 78

2.7.3 Sample Network Application for Traffic Assignment 79

2.7 Travel Demand Model Applications 80

2.7.1 Scoping a Planning Study 81

2.7.2 Travel Demand Modeling Software 81

2.7.3 Activity-Based Models 82

2.7.4 Forecasting Nonmotorized Travel 83

2.7.5 Forecasting Freight and Goods Movements 84

2.8 Practice Problems 85

2.1 Introduction

Planning can be defined as the activity or process that examines the potential of future actions to guide a situation or system toward a desired direction. Transportation planning, which encompasses all modes of transportation, is a very important function of the state Departments of Transportation (DOTs), as well as planning organization at the metropolitan or regional levels.

This part describes the basic process of transportation planning. Transportation professionals use these planning methods to forecast how much traffic is expected in future-year analyses, where that traffic is expected to go, what routes that traffic is expected to take, and what modes of transportation travelers are most likely to choose. These methods aim to predict and estimate how travelers, the human element in any transportation problem, are likely to behave and act based on prior observations and historic trends. As such, planning methods borrow principles from other disciplines, ranging from psychology and sociology, to operations research and network optimization, to estimated behavioral patterns by travelers across a localized area or broader region.

The text presents critical planning concepts and terms and then introduces the reader to the four-step forecasting process used in transportation planning: trip generation, trip distribution, mode choice, and traffic assignment. The discussion includes data needs and sources for planning analyses, as well as mathematical models used to complete various steps in the forecasting process. The part concludes with a discussion of planning applications and software use, as well as practice problems to further explore and apply the concepts presented in the text.

2.1.1 Purpose of Transportation Planning

The most important aspect of planning is that it is oriented toward the future. Although planning may increase the likelihood that a recommended action will take place, it does not guarantee that it will. Transportation planning relies on the use of models and forecasts, which are often wrong, because even the best models can, at best, only approximate future conditions. As such, transportation planning is as much an art form as it is science, placing a constant burden on the analyst to properly interpret model results and apply good professional judgment to any analysis.

State transportation planning organizations are responsible for conducting long-range transportation planning, also known as systems planning, for all areas of the state, including metropolitan areas, small urban areas, counties, and multicounty regions. The metropolitan areas and regions in turn have their own planning organizations that offer a more detailed and in-depth look at transportation plans under their jurisdiction. Ideally, state and metropolitan planning organizations (MPOs) work jointly and in concert to develop robust future-year forecasts based on their combined expertise.

A typical long-range planning study involves several steps, including:

 Initial meetings with the local area citizens, staff, and elected officials

 Data collection and analysis

 Discussions of findings with the local area

 Development of several alternative future scenarios

 Public information workshops and public hearings

 Selection of a preferred plan

The Federal Highway Administration (FHWA) identifies eight critical factors in the transportation planning process, as outlined in Figure 2.1. The FHWA publication emphasizes early on that transportation planning is a collaborative process between all systems of the users. Stakeholders in transportation problems include the business community, the residential community, environmental groups, the traveling public, freight operators, and the general public. As such, the process in Figure 2.1 emphasizes feedback and public input throughout the planning process. Similarly, the reality of fiscal constraints, as well as recognition of sensitive environmental, historic, or socioeconomic areas, make transportation planning a continually evolving and dynamic process.

To accommodate diverse interests and stakeholder groups, planning organizations at the state, regional, and municipal levels often collaborate and exchange data and predictions to arrive at a more accurate and comprehensive final transportation plan to benefit all stakeholders. By first determining the transportation deficiencies, the process attempts to determine the 20-30-year long-range transportation needs for each area at the state level, with...