According to DOT, only 3 percent of traffic signals in the country's largest metropolitan areas are controlled by adaptive signal control.

Adaptive signal control technologies are signals that can be automated to adjust signal timings in real time, allowing for faster responses to traffic conditions caused by special events or traffic incidents. GAO found that despite benefits of adaptive signals, only 3 percent of traffic signals in the country's largest metropolitan areas are controlled by adaptive signal control. According to DOT, agencies have not deployed adaptive signals because of the costs and uncertainty about their benefits. This raises the question of which is more expensive: implementing smart systems and contending with lost productivity, wasted fuel and inconvenience of dumb systems.