I don't get flats nearly as often either, but it does still happen. In fact, on the way to a date with my now wife, I actually had two flats in less than two hours! The first one was caused by a bolt that I apparently ran over in an industrial area. Not sure if it qualifies as a highway or byway, just a 4-lane divided street.
The second was on the 710 freeway, where I imperfectly dodged an accident in progress. Fellow in an older Honda Civic had started to change lanes and then changed his mind, without realizing that a Toyota had already taken his place. Some kind of chrome strip came spinning into my lane, and apparently the end of it caught a sidewall just right. Took another 10 minutes or so to go flat, but the tire was ruined.
Fortunately she was sympathetic, and since I was nearly at her house by the time the second one went flat, she came and rescued me. We had dinner while the shop mounted a new tire.