In this double-blind, crossover trial, randomized to order, recruited participants will be screened and then will accompany the study team on three typical commutes on separate days with sufficient washout (i.e., three weeks) between drives. One day this will occur with an effective filter system in the vehicle and the other two days without effective filtration; ineffective filtration is the most typical actual vehicle condition. Subjects will be unaware of the filtration conditions of the commute on that day. Each subject's experimental sessions will occur at the same time of day and will be separated by at least 21 days. The two sessions (either filtered air or traffic-derived entrained air) will be 120 minutes in duration and will encompass routes on heavily traveled roadways in the Seattle area. Before subjects begin the commute trials, they will go through the consent process and a series of screening tests. The study investigators will assess a series of measures regarding vascular function before and after each drive.
