https://www.google.com/maps/@38.9388432,-77.1037727,3a,60y,288.85h,90.79t/data=!3m6!1e1!3m4!1sJ6YfnXZZk-e6EjHDmSvb2A!2e0!7i16384!8i8192
Usually on 2 way roads, left turns can be banned for safety/congestion reasons. But here right turns are banned 4-6:30pm to avoid congesting a 6 way roundabout, which I think is pretty cool
I think the reason is more to discourage traffic from commuting on local streets like Rockwood Pkwy.