Ramp Metering
The Phoenix freeway system heavily utilizes ramp meters, with 121 currently operational in the metropolitan area. Since their implementation in the 1980s, the goal of these has remained to "break up platoons" of cars by limiting the number that can enter a freeway at a time. The Arizona Department of Transportation (ADOT) states that this has been "tremendously successful".
Read more about this topic: Phoenix Freeways