For those of us who are old enough to remember the pre-NMSL days, speed limits did not mean that much, but, since many of them were set at or near the 85th percentile, compliance was not a major problem. In Louisiana, we have a very poor rate of compliance with 55 and 65 mph speeds. The ostrich approach does not work. People are tired of the oppression, and they see action in other states, but not here. Urban Interstates Speed limits, if any, should be set at or just above the 85th percentile speed, just as they should for rural interstates.
People argue about congestion.
As the highways become increasingly congested, the traffic slows down out of necessity. The problem takes care of itself. Drive through a large city. When the traffic is light, it goes at least as fast as rural interstate traffic. When a freeway is 8 or 10 lanes, it really goes fast.