This factsheet summarizes the final rule for the measurement of non-single occupancy vehicle travel in specific urbanized areas. Initially, the rule applies to urbanized areas of more than 1 million people that are also in nonattainment or maintenance areas for ozone, carbon monoxide or particulate matter. In the second performance period (which begins on January 1, 2022), the population threshold changes to areas of more than 200,000. All States and MPOs with NHS mileage that overlaps within an applicable urbanized area must coordinate on a single, unified target and report on the measures for that area.