“…Inspection/maintenance program smog-check inspections provide data on in-use vehicles, but are inadequate indicators of on-road emissions since the tests are performed over only two no-load engine operating conditions (2500 rpm and idle). While more recent research has focused on correlating driving mode with emissions (Hansen et al, 1995;Jensen, 1995;Joumard et al, 1995;Sjodin and Lenner, 1995;Barth et al, 1997;Washington et al, 1997;Young et al, 1997), emissions were usually estimated from emission models rather than measured directly in the ®eld. The few studies that have used on-board gas analyzers (Schurmann and Staab, 1990;Kelly and Groblicki, 1993;Guenther et al, 1996) demonstrated the capabilities of these instruments to measure second-by-second emission levels to aid in repair of malfunctioning emission systems, but made no e ort to correlate driving style and emission levels.…”