I'm not so sure it is nonsense. Those rural 50mph roads are generally considered the most dangerous road type and many states prioritize turning them into actual divided roads due to prevalence of fatal accidents. Admittedly the rush hour traffic experience depends a lot on where you live; in the midwest you probably only see congestion on the exit itself and are otherwise going the full 60mph on even urban freeways, whereas in places like LA or NYC you aren't breaking a 16mph average no matter what road you are on during rush hour. Not a lot of ways to die going 16mph...