On January 13, 2011, EPA posted the latest version of the method for estimating re-entrained road dust emissions from cars, trucks, buses, and motorcycles on paved roads. This document approves this method for use in PM<INF>10</INF> and PM<INF>2.5</INF> state air quality implementation plans (SIPs) and regional emissions analyses for transportation conformity determinations ("regional conformity analyses"). This new method is incorporated in Chapter 13 of Compilation of Air Pollutant Emission Factors, AP-42, Fifth Edition, Volume I, that was published in January 2011. Today's action also starts a two-year grace period after which the January 2011 AP-42 method is required to be used in regional conformity analyses in PM<INF>10</INF> nonattainment and maintenance areas and any PM<INF>2.5</INF> nonattainment and maintenance areas where the EPA regional administrator or the state air quality agency determined that re-entrained road dust is a significant contributor to the area's PM<INF>2.5</INF> problem, or if the area has a PM<INF>2.5</INF> motor vehicle emissions budget that includes re-entrained road dust. This document is not relevant to SIP development or regional conformity analyses for ozone, carbon monoxide, and nitrogen dioxide nonattainment and maintenance areas, or for areas that use EPA-approved locally developed road dust methods.