The objective of this study was to model the potential impacts of alternative transit-oriented urban design scenarios on community exposures to roadway air pollution. We used a modeling framework developed previously for the study area that includes activity-based travel demand modeling (Tampa Bay ABM), a dynamic traffic assignment model (MATSim), a mobile-source emissions model (MOVES), a line-source dispersion model (RLINE), and a population exposure estimator to simulate ambient concentrations and population exposure to oxides of nitrogen (NOx) under alternate urban design scenarios for Hillsborough County, Florida. Data from the 2040 transit plan envisioned by the Tampa Bay Area Regional Transportation Authority were added to the modeling system along with reassignment of household residence locations to parcels near to both employment centers and transit stops. Scenarios included a low-transit scenario (S1) that used the 2040 base residential distribution with 2010 bus services, an enhanced-transit scenario (S2) that applied the proposed 2040 bus services, and a compact-growth scenario (S3) that increased the residential density in S2 by redistributing 37% households to be near to jobs and bus stops. Results show slightly higher shares for active modes of travel for S2 and S3 compared to S1, with an increase of 7.1% for walking and 1.8% for transit under S3 specifically. Measures of travel under S3, including daily total travel distance and travel time, decreased compared to S1 by 9% and 2.1%, respectively. Pollution results were more mixed. Daily total emissions of NOx and its overall mean ambient concentration were lower for S3 than S1 (by 11% and 9%, respectively), but mean population exposure was higher (by 29%), due to the collocation of people and pollution. Enhanced diesel bus services alone increased emissions, concentrations, and exposures to NOx. This study suggests that a multi-faceted approach may be needed to ensure beneficial pollution outcomes of transportation and urban design interventions.