Section 11205 of the Bipartisan Infrastructure Law required the U.S. Department of Transportation to promulgate best practices to better account for induced demand in travel demand modelling and support state and MPO capacity to increase model accuracy. In response, the U.S. Department of Transportation published a set of preliminary best practices as part of the Climate Strategies that Work.

This overview will cover that BIL section and best practices document, the current state of administrative policy on travel demand, political considerations, and future opportunities to advance increased modelling accuracy at the state level.

A project for the National Cooperative Highway Research Program (NCHRP) is underway to develop an induced demand assessment framework and a guide to help Departments of Transportation (DOT) to apply framework to policy and planning analysis.  The research objectives include (1) defining induced demand; (2) gathering and evaluating data needed to develop the assessment framework; (3) piloting, validating, and testing the assessment framework; and (4) communicating findings from the framework to build consensus.

In contrast to analysis of aggregate-level data, the research team is using a “case study” approach to evaluate major highway capacity and operations improvement projects across different geographic contexts. This approach involves examining data sources specific and appropriate to each project context.  The case studies will provide a comprehensive view of the elements influencing high or low induced demand response as a function of project scope.  The case study locations will be selected using four key criteria: 1) geographic/contextual diversity; 2) projects completed within the past 5 to 10 years; 3) likely availability of suitable data; and 4) willingness of the state DOT to assist with data collection.

The research team has completed an exhaustive literature review, covering over 25 years of studies and developed a working definition of induced travel, which may be simply stated as “changes in the amount and nature of travel resulting from changes in the transportation system.”  We note that induced travel has several components, including shifts in route, mode, time of day, and trip destination, as well as changes in the number of trips and land use development impacts.  However, these components are not always easy to distinguish within the context of observed data.

The literature review reveals some areas of broad consensus and the ongoing evolution of understanding regarding induced travel as research has advanced over the years.  Several gaps in the existing research have been identified, including how induced travel effects may vary within different project contexts, how travel speeds affect travel volumes, how the various components of travel change contribute to overall observed induced travel effects, the degree to which induced travel applies to commercial vehicle travel, and the degree to which the underlying components of induced travel are changing over time.  The research team is working on filling these research gaps as possible.

At the time of the presentation, the research team will have nearly completed the analysis of relevant data and will be close to proposing specific case study locations to the project panel.  The case study approach will be fully delineated, and the analysis methods will have been defined.  The presentation will be designed to solicit input from the planning and modeling communities; this will help greatly to inform the case study work and the guidance developed over the following year.

In response to Senate Bill 743 (Steinberg, 2013), and the subsequent decision by the state to apply the legislation statewide, and the guidance issued by the Governor’s Office of Planning and Research, the California Department of Transportation (Caltrans) determined that Vehicle Miles Traveled (VMT) was the metric for determining transportation impacts of capacity increasing projects on the state highway system (SHS). This paper examines methodologies for assessing induced Vehicle Miles Traveled (VMT) in the context of California’s SB 743 policy.

The Caltrans Transportation Analysis Framework (TAF) outlines two approaches for estimating induced travel: an empirical method employing the National Center for Sustainable Transportation (NCST) Induced Travel Calculator and a regional or local travel demand model. The NCST Calculator quantifies long‐term induced travel by applying long-term average elasticities based on empirical (before-after) studies from national databases and Caltrans-endorsed research. The NCST calculator relies on the addition of lane miles but does not directly account for any VMT change associated with population and employment growth, change in demographic or socioeconomic conditions, advances in transportation technology or modes, etc. In contrast, the travel demand models model incorporates diversion effects and changes in origin–destination patterns to capture both short-term and, with current land use assumptions, long-term impacts of highway capacity enhancements; however, it lacks sensitivity to the land use response to network changes.

The long-term elasticities are inherently variable across projects, corridors, and regions, and the NCST Calculator’s reliance solely on lane-mile additions may lead to estimation biases in corridors with unique travel characteristics. Through a series of case studies in urban corridors, this study compares VMT estimates from the NCST tool and an activity-based model, and explores hybrid approaches for reconciling short- and long-term induced travel effects in capacity-assessment projects. The findings underscore the importance of considering corridor context and the inherent limitations of each method when interpreting induced VMT estimates.