Quoted from: https://www.epa.gov/scram/air-quality-dispersion-modeling-alternative-models#hyroad 

The HYbrid ROADway Model (HYROAD) integrates three historically individual modules that simulate the effects of traffic, emissions and dispersion. The traffic module is a microscale transportation model which simulates individual vehicle movement. The emission module uses speed distributions from the traffic module to determine composite emission factors; spatial and temporal distribution of emissions is based on the vehicle operation simulations. The model tracks vehicle speed and acceleration distributions by signal phase per 10-meter roadway segment for use in both emissions distribution and for induced flows and turbulence. The dispersion module uses a Lagrangian puff formulation, along with a gridded non-uniform wind and stability field derived from traffic module outputs, to describe near-roadway dispersion characteristics. HYROAD is designed to determine hourly concentrations of carbon monoxide (CO) or other gas-phase pollutants, particulate matter (PM) and air toxics - in consultation with appropriate Reviewing Authority - from vehicle emissions at receptor locations that occur within 500 meters of the roadway intersections.