Making Strides: State of the Practice of Pedestrian Forecasting in Regional Travel Models

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Transportation Research Record

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Much has changed in the 30 years since non-motorized modes were first included in regional travel demand models. As interest in understanding behavioral influences on walking and policies requiring estimates of walking activity increase, it is important to consider how pedestrian travel is modeled at a regional level. This paper evaluates the state of the practice of modeling walk trips among the largest 48 metropolitan planning organizations (MPOs) and assesses changes made over the last 5 years. By reviewing model documentation and responses to a survey of MPO modelers, this paper summarizes current practices, describes six pedestrian modeling frameworks, and identifies trends. Three-quarters (75%) of large MPOs now model non-motorized travel, and over two-thirds (69%) of those MPOs distinguish walking from bicycling; these percentages are up from nearly two-thirds (63%) and one-half (47%), respectively, in 2012. This change corresponds with an increase in the deployment of activity-based models, which offer the opportunity to enhance pedestrian modeling techniques. The biggest barrier to more sophisticated models remains a lack of travel survey data on walking behavior, yet some MPOs are starting to overcome this challenge by oversampling potential active travelers. Decision-makers are becoming more interested in analyzing walking and using estimates of walking activity that are output from models for various planning applications. As the practice continues to mature, the near future will likely see smaller-scale measures of the pedestrian environment, more detailed zonal and network structures, and possibly even an operational model of pedestrian route choice.

A growing number of U.S. metropolitan planning organizations (MPOs) have incorporated walking and other non-motorized modes into their regional travel demand forecasting models (1). These models are used for long-range planning, allowing regions to analyze land use and transportation scenarios and projects for their impacts on walking and bicycling. Models that can forecast walking also have many other applications. In the short term, they are useful for prioritizing non-motorized infrastructure investments. In the long run, models that are sensitive to how the pedestrian environment influences travel behavior could better predict mode shifts and the resulting impacts on motor vehicle emissions of greenhouse gases and other air pollutants. Regional pedestrian models can also inform traffic safety analyses and health impact assessments, providing required estimates of the location and number of walk trips.

Partly in response to these new policy demands and partly due to advances in computational power, travel demand models are becoming more sensitive to finer-grained representations of travelers themselves and the environments through which people travel. The growing number of implemented activity-based models is one example of this evolution. Two other major trends support these modeling enhancements. First, archived spatial data on the built environment are becoming ubiquitous, allowing small-scale, pedestrian-relevant environmental measures to be included in models (2). Second, research on pedestrian travel behavior and its environmental determinants has advanced to the point of offering at least initial guidance about which relationships may be important to represent (3, 4).

In the face of these trends and opportunities, MPOs have taken various approaches to characterizing walk trips in their travel demand models. The purpose of this study is to assess the state of the practice with respect to how pedestrian travel is incorporated into these regional models; specifically, this paper reviews if and how the largest 48 MPOs model walk trips. The authors assess frameworks, spatial scales, behavioral and environmental data, applications, challenges, and innovations. This paper offers agency and consultant staff a better understanding of how regional pedestrian modeling is currently done and how it might evolve in the future, so that they can adapt techniques and improve their own models. It also serves as an update to several other recent (and not-so-recent) reviews on this topic (1, 5–8).

A few notes about the scope of this study are warranted. First, although the focus of this paper is on walking or pedestrian travel, some of its results may also be relevant for bicycle modeling. Walking and bicycling modes have been frequently lumped into a single “non-motorized” mode for modeling purposes. This practice is starting to change, and bicycle modeling has in some ways eclipsed pedestrian modeling, especially in the area of route choice and trip assignment procedures. We encourage interested parties to examine the state of the practice of regional bicycle modeling in more detail (9–11), as this is beyond the scope of this study. Second, we focus on “pure” walk trips, not instances of walking linked to accessing other modes. Modeling practices for walk-access-to-transit trips are relatively well-established, although they may still benefit from some of the discussions here. Third, this paper is narrowly focused on large MPO regional forecasting models. We acknowledge that many modeling innovations are taking place at sub-regional scales and through smaller and non-MPO agencies, including the use of sketch-planning and accessibility-based tools (12–15). Some of these standalone pedestrian planning tools may be easier to develop, more agile to apply, or better suited to addressing certain policy questions, or both, than are regional travel demand models (14), yet we leave this subject for others to address. Fourth, our objective is to provide a broad overview of the state of the practice, therefore, we do not have the space to describe specific case studies in depth. A number of other pedestrian modeling resources (8, 14, 15) include such case studies, and we encourage interested readers to contact the MPOs we describe throughout this paper for more information on their respective practices.

The remainder of this paper begins with a Background giving a brief history of non-motorized and pedestrian modeling practices and trends. Next, a short Method section describes the state-of-the-practice survey and analysis procedures. The Results section then presents and discusses findings regarding pedestrian modeling frameworks, spatial scales and networks, and built environment measures. It also discusses barriers and challenges as well as model applications. The paper concludes by summarizing the major contributions of this work, describing innovative pedestrian modeling practices, and noting opportunities and directions for the field.


© National Academy of Sciences: Transportation Research Board 2018