I'm the PP with the work colleague who did this. This was their younger child. The older child had already graduated. I also have an elementary age kid which is one reason it would not work for us.
We only live 5 miles away, but it takes my child over an hour on the bus in the afternoons to get home. It's only 15 minutes in the morning when I drive them. For us, it makes no sense, but if my kid lived in Chantilly north Reston near Sterling....well I can see the appeal.
And for some people the choice is more like TJ vs. a private school that may cost >$30,000 a year. That's a very different calculation.