Adaptive traffic control
Adaptive traffic control system (ATCS) is a traffic management strategy in which traffic signal timing changes, or adapts, based on actual traffic demand.  This is accomplished using an adaptive traffic control system consisting of both hardware and software.

Every Day Counts initiative
The U.S. Federal Highway Administration, through its Every Day Counts initiative, is working to accelerate the adoption of adaptive signal control technologies in the U.S.  Its website states, "Real-time management of traffic systems is proven to work, yet these systems have been deployed on less than 1 percent of existing traffic signals. FHWA is now working to bring these technologies to the rest of the country."

Examples
InSync adaptive traffic control system is a real-time adaptive traffic control system that enables traffic signals to immediately adapt to traffic demand.

MASSTR (Meadowlands Adaptive Signal System for Traffic Reduction) located in the Meadowlands Region of northern New Jersey will incorporate over 128 signals when complete. As of June 2013, over 50 of the signals were operational. The project built by the New Jersey Meadowlands Commission (NJMC) is a network self-adaptive signals utilizing the Sydney Coordinated Adaptive Traffic System (SCATS). MASSTR was awarded a $10 million TIGER2 grant from the Federal Highway Administration.

MOVA (Microprocessor-Optimised Vehicle Actuation) uses inductive loops in the carriageway to detect traffic on each approach to an isolated junction, and vary the signal timings as required.

See also
 SURTRAC adaptive traffic control system
 SCOOT
 Adaptive Traffic control system using AI - Pushpak.ai

References

External links
Official site of the Federal Highway Administration
AI for calculating density of vehicle presence on road 

Traffic signals