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Guidebook on Methods to Estimate Non-Motorized Travel: Overview of Methods

1.0 Introduction

1.1 Purpose of Guidebook

The need for improved conditions for bicyclists and pedestrians has received increasing attention in recent years in transportation planning circles. Planners are recognizing a growing popular interest in bicycling and walking for health and recreation, the desire to promote alternatives to automobile travel for environmental reasons, and the need to provide safe and convenient travel options for the entire population. At the same time, the question of how many people will actually use new or improved bicycle and pedestrian facilities is gaining attention and importance. Planners and policy makers need to be convinced that the benefits of improvements are worth the costs. Furthermore, they want to know where to spend limited resources to get the most "bang for the buck" as measured by benefits to users.

This guidebook was developed in response to the need to predict bicycle and pedestrian or "non-motorized" travel. The guidebook is intended to provide a means of addressing the following related questions:

• If we build a new bicycle or pedestrian facility, how many people will use it?
• If we improve an existing facility or network, how many additional people will choose to walk or bicycle?
• What types and combinations of improvements will have the greatest impact on increasing non-motorized travel?
• How will improvements to non-motorized travel conditions affect motor vehicle use?

The guidebook describes and compares the various methods that have been developed to predict future levels of bicycle and pedestrian travel, i.e., "travel demand." The guidebook also discusses other quantitative methods that support demand forecasting but do not actually predict future demand. These include (1) analyses of the potential market for bicycling and walking; (2) " level of service" measures and "environment factors" which describe the quality of the supply of bicycle and pedestrian facilities; and (3) supporting tools and techniques such as Geographic Information Systems (GIS) and preference surveys. The guidebook is intended to be used by bicycle and pedestrian planners, technical staff, researchers, advocates, and others who may wish to apply these methods to estimate bicycle and pedestrian travel demand and/or to prioritize bicycle and pedestrian projects.

Figure 1.1: If We Build a New Bicycle or Pedestrian Facility, How Many People Will Use It?

While all of these methods focus on non-motorized travel, some important distinctions in scope can be identified. Some methods are directed specifically at either bicycle or pedestrian travel, while others are generally relevant to both. Some methods focus on demand for a specific facility, such as a bicycle lane or shared-use trail, while others focus on travel over an entire area, such as a city or census tract. Finally, the methods differ in the extent to which they consider trips made for recreational, as opposed to utilitarian, purposes(2).

The guidebook is based on an extensive international review of both published and unpublished sources. Most of the methods were developed in the United States and Europe, but examples are also included from Japan, Australia, and South America. While it is doubtless that some relevant sources and methodologies have been overlooked, the guidebook should serve as a reasonably complete review of methods currently available to the bicycle and pedestrian planner.

1.2 The Importance of Forecasting Demand

There are many compelling reasons both to apply existing methods of forecasting bicycle and pedestrian travel and to advance the state-of-the-practice in this area. If properly done, demand forecasting has a variety of uses including:

• Estimating the benefits of a proposed project, such as number of users served, reductions in automobile emissions and energy consumption, or time and cost savings to travelers;

• Prioritizing projects based on the greatest benefit to existing users or on the greatest payoff in attracting new bicyclists or walkers;

• Planning bicycle or pedestrian networks and identifying and correcting deficiencies in existing networks, based on desired travel patterns and facility characteristics; and

• Planning for bicycle and pedestrian safety by developing exposure information for crash/safety models. In the United States in particular, two recent developments underscore the importance of quantifying demand:

• The 1994 U.S. Supreme Court Dolan vs. Tigard decision. This decision mandates that local jurisdictions quantify proposed bicycle project benefits when the project involves private land dedications under master plans.

• The 1998 passage of the Transportation Equity Act for the 21^st Century (TEA-21). TEA-21 continues and expands provisions of its predecessor, the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA), to improve facilities and safety for bicycles and pedestrians. TEA-21 places an emphasis on quantifying the air quality and congestion alleviation benefits of projects, including bicycle and pedestrian projects to receive funding under the Congestion Mitigation and Air Quality (CMAQ) program(3). TEA-21 also adds "bicycle transportation and pedestrian walkways" to the list of eligible projects for National Highway System Funds and expands eligibility for funding under other programs(4). Estimates of the benefits of bicycle and pedestrian projects will be useful in competing for funding under these programs.

All of these reasons underscore the need to apply available demand forecasting methods and to continually advance these methods. Forecasts of demand provide a much needed complement to other considerations, such as improvements to safety and convenience for existing users, in planning bicycle and pedestrian facilities.

Nevertheless, many people in the bicycle and pedestrian planning and advocacy communities are skeptical of demand forecasting, and raise valid points about its limitations. Skeptics argue that the factors influencing non-motorized travel are largely attitudinal and cannot be easily described or quantified in models. They further believe that comprehensive efforts to improve facilities, policies, and social attitudes toward bicycling and walking are required, and that such measures would result in significant mode shifts that would not be predicted by existing models. Others take the philosophical viewpoint that conditions for bicyclists and pedestrians should be improved simply as a matter of fairness to existing users, regardless of whether new users would be attracted. Still others are concerned that a focus on predicting demand will divert much needed energy away from the actual implementation of bicycle and pedestrian improvements.

These arguments, although valid, should not detract from the usefulness of forecasting bicycle and pedestrian travel demand. A simple "if you build it, they will come" attitude is not sufficient given that resources for implementing projects are limited. Existing forecasting methods, even given their limitations, can help allocate resources toward the most beneficial projects and can help determine which improvements will attract the most new users. Furthermore, future developments have the potential to greatly increase the accuracy and usefulness of these methods. While qualitative assessment based on experience and judgment will continue to play a key role in identifying projects with the greatest benefits, quantitative methods can become increasingly useful in providing information for planning and decision making.

1.3 How to Use This Guidebook

This guidebook consists of two parts: Overview of Methods and Supporting Documentation. Overview of Methods provides a concise overview of the available methods and of general issues for consideration in forecasting demand for non-motorized travel. Supporting Documentation provides substantially more detail on the methods described in the guidebook and identifies sources and real-world applications for the methods.

The contents of Overview of Methods include:

• Section 2.0- An introduction to non-motorized travel demand forecasting, including ways in which travel behavior can change, general approaches to travel demand forecasting, factors specifically influencing bicycle and pedestrian travel, and differences in forecasting bicycle vs. pedestrian travel.

• Section 3.0 - An introduction to 11 classes of methods, and a one-page overview of each which includes a description, typical applications, advantages, and disadvantages. Section 3.0 also contains a summary of key characteristics and uses of each method as well as a guide to choosing an appropriate method for a specific purpose.

• Section 4.0 - A summary of this guidebook and a discussion of the limitations of existing forecasting methods and future research needs for improving non-motorized demand forecasting.

Supporting Documentation includes:

• Section 1.0 - A description of the research methodology and a categorization of the methods according to their major purposes.

• Section 2.0 - An in-depth, structured description (e.g., purpose, structure, inputs/data needs, assumptions) of each method along with evaluative criteria. Multiple variations on some methods are included, as well as specific examples and real-world applications.

• Section 3.0 - An annotated bibliography of references on demand forecasting methods, supporting tools and techniques, and factors influencing the choice to walk or bicycle.

• Section 4.0 - A list of individuals and organizations contacted in developing this guidebook.

¹Bicycling and walking are the most common forms of non-motorized travel in most countries and the term "non-motorized" is used herein to refer collectively to bicycle and pedestrian travel. Nevertheless, the term "non-motorized" could also refer to many other forms of travel such as in-line skating, skateboarding, or horseback riding. The methods discussed in this document may be applicable to these other forms of non-motorized travel although specific applications have not been identified.
²A significant weakness of existing methods is that none differentiate explicitly between utilitarian and recreational travelers. The two travel markets have very different characteristics and needs, and a greater focus on these distinctions would help improve the accuracy and usefulness of travel forecasting methods in the future.
³Title I, Sections 1110.
⁴Title I, Sections 1106 and 1202.

FHWA-RD-98-165