Salt Lake City has no traffic. They use one second stop lights on entrance ramps. There is no way a highway can absorb 20 new cars entering the system without slowing down. One car per second lets the flowing highway absorb new vehicles without slowing down. All traffic keeps moving at highway speeds.
Austin's 'On-ramps' need to be separated from the 'exit-ramps'. Many people exit and enter all the way down the highway. This happens worst at town lake driving north. People exit over the lake and reenter immediately after the lake, slowing everyone else that stays on the highway.