Transportation infrastructure is important for human mobility and population well-being. However, it can also have detrimental impacts on health and equity, including through increased air pollution and its unequal social distribution. There is a need for better understanding of these impacts and for better approaches that improve health and equity outcomes of transportation planning programs. In this study, we are investigating the air pollution and health equity impacts of an ongoing large-scale metropolitan transportation improvement program, Tampa Bay Next (TBNext). Specific objectives are: 1) to characterize and quantify the air pollution levels and population exposures resulting from the roadway expansion currently planned under TBNext, and 2) to identify key attributes that could improve health and equity consideration in TBNext and similar programs. Using a multi-component modeling system that combines agent-based travel demand simulation with air pollution dispersion estimation, we simulated population exposures to oxides of nitrogen (NOx) resulting from two scenarios: one with the proposed TBNext lane expansions and one without it. To elucidate potential impacts on equity, including disparities in exposure for low-income and minority groups, the distribution of exposure among the population was compared using three measures of inequality. Additionally, through document review, we also performed a qualitative analysis of the TBNext program from a Health in All Policies (HiAP) perspective. Results from the modeling component indicate that the proposed lane scenario increased the number of vehicles, NOx emission rates, NOx concentration, and block group NOx exposure densities in downtown Tampa and its surrounding neighborhoods during the morning and evening rush hours. However, the proposed lanes also caused a decrease in the simulated total emissions and the daily average NOx concentration in Hillsborough County. The average individual-level NOx exposure also decreased, but disparities in exposure for minority and the below-poverty population groups increased in the proposed lane scenario. Results of the HiAP analysis suggest that health and equity should be priorities in major policies and programs such as transportation improvement programs. Multi-sectoral collaboration that provides benefit for all parties and stakeholders is also essential to improve the health and equity outcomes. Furthermore, health departments and public health agencies should be included in the transportation decision-making process. Finally, improving active transportation modes was commonly found in HiAP case studies to promote public health and equity in transportation planning programs. Evaluation of TBNext transportation improvement program from the HiAP perspective show that health consideration was not one of the priorities in the program. However, the Florida Department of Transportation (FDOT) frequently engaged with stakeholders in community meetings throughout the recent development process of the program. Additionally, FDOT and local governments addressed some inequity issues as a response to public concerns. Through assessment of a real case study, the results of this study contribute to the body of knowledge on the air quality and equity impacts of large-scale transportation improvement programs. Further, they suggest that air quality assessments and equity analyses should be conducted in more detail than what the law currently requires for transportation programs. Lastly, this study also shows that the HiAP paradigm could promote health and equity outcomes of transportation improvement programs.