That actually doesn't make cigarette smoke seem all that bad, to me (for those too lazy to read, it compares one tailpipe to 3 cigarettes, the cigs are 10x worse for particulates).
If each cigarette is equivalent to about 10 minutes of a car running, and assume the average smoker does 15 cigarettes a day... that's 2.5 hours' worth of tailpipe exhaust. Which is likely about what the average driver drives, easily these days.
So being in traffic for a couple of hours each day is like being nearly a pack a day smoker. Whoulda thunk?