Introduction

Critical Issues in Transportation for 2024 and Beyond is authored by the Executive Committee of the Transportation Research Board of the National Academies of Sciences, Engineering, and Medicine (the National Academies). Editions have been published on a 2- to 5-year cycle since 1976. This publication reflects the collective judgment of the members of the Executive Committee regarding issues of priority concern at the time of publication. Critical issues are defined as those that have a significant impact on achieving societal goals across all modes. These issues are unresolved matters of debate or concern or are important and difficult problems or questions that can be informed by research and addressed through innovation and public policy. The issues can be long-standing or emergent, hence the shifting topical focus across editions of this publication over time. The statements in bold font at the end of each section reflect our attempt to frame the core of the problem or source of contention. Past editions of Critical Issues in Transportation were intended to foster awareness, debate, and research rather than provide solutions to the sometimes contentious issues they identified. This edition is offered in the same spirit. It identifies issues and raises concerns that can be addressed through research and development (R&D) (identifying and filling critical research gaps) and policy decisions but does not offer recommendations by design.

The approach taken in this edition is a departure from past practice. Rather than a lengthy list of critical issues grouped by topic, we have illustrated the importance of selected issues by relating them to the achievement of vitally important societal goals. Although this publication spans all modes of transportation, as well as research and innovation across all modes, government-funded surface transportation research tends to set priorities

based on specific problems that practitioners face, thereby resulting in tractable but narrowly defined topics.¹ Such research may ultimately serve societal goals by advancing the state of practice in surface transportation. However, setting priorities from a “bottom up” perspective may neglect more important topics and frame research questions without appreciating how much the success of transportation policies and programs depends on accounting for the interrelated influences of the foundational factors and policy levers identified in Figure 1. In contrast, we describe selected critical issues to encourage setting priorities for transportation research and innovation. These critical issues are rooted in societal goals and framed in ways that will help the transportation sector contribute toward achieving these goals. Fully covering transportation’s role in serving each of the five societal goals would span multiple technical literatures and require a much longer publication. Hence, we have used our judgment in identifying a limited number of topics and addressing them at a high level. There are many other important policy issues involving transportation that require further research. We encourage readers to explore the wealth of Transportation Research Board and National Academies’ publications on these issues and the many dimensions of the critical issues described therein.² Also unlike previous editions, this edition relies heavily on metrics whenever possible to support inclusion of a topic and to show progress, or not, in addressing the societal goals identified. Readers are encouraged to explore alternative metrics and means of filling data gaps that can help the transportation community better contribute to a thriving society. Further development of metrics for monitoring progress is outlined in the Appendix.

The sections that follow describe transportation’s influence on each of the societal goals as well as transportation’s dependence on the foundational factors and policy levers depicted in Figure 1. This publication begins with a brief overview of the movement of people and goods in the United States, describing the modes of travel and their energy requirements for passengers and freight. The next five sections discuss how the movement of people and goods supports achieving the articulated societal goals. After next describing the condition and performance of the nation’s transportation infrastructure, the five sections that follow focus on critical issues among the foundational factors and policy levers that influence transportation’s success or failure in supporting the five societal goals. These sections refer only to direct benefits and costs. Students of transportation recognize that it has benefits and costs that cannot be easily monetized, and no attempt to do so is made in this publication. Instead, it highlights both transportation’s positive and negative aspects. The final section summarizes the challenges to be overcome in maximizing transportation’s positive role in contributing to a thriving society.