(I should have posted this two weeks ago. Oh well.)
Sandy left to go shopping on Monday, the fifth of July. She called me a few minutes later because she had a flat tire. Actually, the tire was flat before she left the driveway, but she didn't notice.
We were lucky in two ways: the tire and rim didn't get ruined and a neighbor saw her drive (limp?) by and followed her. I was happy to have the help. (Thanks Richard!)
The problem was what you see below:
I'm glad that 16d common nails aren't that common on the road.