The paper gives results of a July 1994 mobile emissions study, in Nashville, Tennessee, using an optical remote sensing unit and an instrumented vehicle. Emissions data were collected from approximately 41,000 vehicles over a 2-week period at 11 predesignated sites through the Nashville ozone non-attainment area. The instrumented vehicle was used as a calibration cross-check from the remote sensing unit and as a means of identifying the impact of transportation system features on vehicle emissions. Results from the remote sensing indicate that exhaust concentrations in the Nashville fleet are essentially the same as those previously reported for Atlanta, Georgia.