"The road started out as freeway but quickly became a rural highway, one lane in each direction. The speed limit was 45 or 50mph, fairly fast for that kind of road, it was quite busy and I was in a line of cars doing the speed limit."

I'd be hard pressed to call a rural area a residential neighborhood.

> "I passed a little outpost of houses whose mailboxes were on the opposite side of the street."

I used to live on a road like this, it's not exactly a neighborhood like in most cities (so "residential neighborhood" may not have been accurate) - it's a linear neighborhood along the road. We were lucky enough to have our mailbox at the end of our driveway, not across the street; if our mailbox had been across the street, it would have been unsafe to walk and get the mail.

I live on a street like this with my mailbox on the opposite side of the street. In the winter, I always get my mail a day late since I refuse to retrieve it in the dark. Speed limit is 25mph but average speed is closer to 40mph. City can't be bothered to enforce the limit no matter how much we demand it. Sidewalks are being considered and might finally go in sometime before 2030.

I agree, it's a very poor design, likely dating from an era when high speed was a big noisy horse drawn carriage.

The proper engineering solution to this is to have an angled turn-off on to a side road (either perpendicular or parallel) which /is/ limited to a "safe residential speed".