I hate car exhaust, it's the main reason I will filter up to the front of the line. Diesel is the worst. The local BusCo finally got rid of their GM diesel busses with the street level exhaust a few years ago, that makes things a lot better, but there are still a lot of diesel delivery trucks w/ street level exhaust, not to mention all the pseudo contractor yahoos with Dodge/Ford/GM diesel pickups (Mercedes too).

edit: I would credit exposure to exhaust fumes while cycling at least in part on my development of asthma as an adult.