Traffic adaptive systems are computer systems that coordinate traffic signals by continually monitoring traffic volumes and making updates to the coordination plan every few seconds.  The concept is intended to provide ideal traffic signal operations through a corridor with multiple traffic signals.  A dozen years ago there were very few adaptive systems deployed in the US, and these were mostly in large cities with very high volumes of traffic.  Now a large number of systems have been deployed.  
A map of existing systems is available at https://maps.google.com/maps/ms?msid=205973504609422839421.0004a0e17d62c903118a7&msa=0&ll=43.644026,-98.4375&spn=26.898865,67.631836