I decided to do four laps on the level track and see how my VO2 Max estimate would compare to the hillier neighborhood route of the other night. So I walked four laps on the kind of soggy track as fast as I could, and I knocked about seven seconds off my time of the other night, down to 13 minutes and 17 seconds. And my heartbeat was slightly lower than before at 140. The overall result was that my VO2 Max level rose slightly to 36.01. That is still on the high end of "good" for males of my age. To get to "very good," my heart rate for the same time in the mile would have to be about 133. To reach "excellent," my heart beat would have to be at 114 for the same time.
If nothing else, just trying to walk a mile as fast as you possibly can is great exercise. My normal walking pace right now seems to be about 14:30 to 14:45 per mile, so cutting 1.25 to 1.5 minutes off of that requires a lot of effort. I'll be evaluating ways to improve my level of cardiovascular fitness in the coming months.
Now, the rest of the story. About a minute after I finished my laps, I was cleaning gravel out of my shoes, and a police officer appeared. He told me that the school had called in a concern that I was on school property and that I had to leave. I apologized and left immediately. I only walked there because the two women were, so I figured that it was all right. Interestingly, the two women continued to walk and run, and the officer left without speaking to them. I guess women are not viewed as the potential threat that men are, with some level of justification, I suppose.