A Retrospective Analysis of Heavy-Duty Vehicle Tailpipe Nitrogen Oxides Emissions Standards

This paper presents a retrospective analysis of the Environmental Protection Agency (EPA) 2007 regulations targeting NO_x emissions from heavy-duty vehicles. We replicate EPA's on-road emissions model and compare the assumptions used in its analysis-vehicle sales, scrappage rates, NO_x emission rates, and vehicle use-with actual outcomes in 2022. This comparison evaluates the accuracy of EPA's assumptions and their long-term impact on NOx reduction estimates, providing a basis to assess the accuracy of the similar methodology used in the recent 2022 standards. We find that EPA's most significant prediction error was overestimating scrappage rates of older vehicles, which led to underestimated emissions both with and without the policy; on net, this resulted in an underestimation of emissions reductions by 0.52 million tons. Conversely, EPA underestimated miles traveled by older vehicles, which, on net, overestimated emissions reductions, as these high-emission vehicles traveled more than expected. Anticipatory sales effects before 2007 had minimal effects on emissions in 2022. Although certified emissions have consistently been below required standards, this discrepancy had only a minor effect on EPA's overall emissions predictions.

Nafisa Lohawala

Fellow

Nafisa Lohawala

Joshua Linn

Senior Fellow

Josh Linn is a senior fellow at RFF. His research centers on the effects of environmental policies and economic incentives for new technologies in the transportation, electricity, and industrial sectors.

Lucie Bioret

Research Analyst

Lucie Bioret is a research analyst at RFF.

Emma DeAngeli

Research Associate

Emma DeAngeli is a research associate at Resources for the Future.

Nicholas Roy

Research Associate

Nicholas Roy is a research associate at Resources for the Future, where he analyzes policies that include clean energy tax credits, renewable energy standards, and emissions pricing.

Beia Spiller

Fellow; Director, Transportation Program

Beia Spiller is a fellow and the director for RFF's Transportation Program. Her recent research has focused around electric vehicles and environmental justice, exploring some of the most pressing issues around electric car, truck and bus adoption.

Working Paper - Nov 3, 2025

Looking at Federal Environmental Regulating Agencies

Through eight analyses, Resources for the Future offers a road map for institutionalizing retrospective analysis as a standard component of regulatory evaluation.

Working Paper - Nov 3, 2025

Administrative Initiatives to Advance Retrospective Analysis

This paper outlines five possible approaches that a new administration could take to advance retrospective analysis.

Working Paper - Nov 3, 2025

Congress's Role in Promoting Environmental Policy Evaluation

This paper identifies ten key barriers hindering robust environmental policy evaluation in federal agencies and, drawing on ex-post review experience, analogous efforts, and interview insights, proposes a range of congressional reforms at varying levels o

Working Paper - Nov 3, 2025

Are "Killer Trees" Helpful for Understanding the Effects of the NOx Budget Program?

This paper examines how preexisting air quality affects the ability of air pollution policies to reduce ground-level ozone, which has variety of health impacts, especially on vulnerable populations.