Deploying intelligent transportation systems (ITS) is one way that state and local transportation agencies have attempted to address issues related to traffic safety and congestion. ITS consists of sensors, computer hardware and software, and communications systems that, for example, automatically change the timing of traffic signals (“adaptive signal control technology”).
According to Department of Transportation (DOT) 2020 surveys of state and local agencies, some technologies are widely deployed on arterials (roads with traffic signals) or freeways, while others are less widely deployed. Examples of widely deployed technologies include dynamic message signs, which provide information to travelers; technologies that detect vehicles and other roadway users to provide information on traffic flow; and emergency vehicle preemption, which provides green lights to emergency vehicles (see figure). Examples of technologies deployed by less than 30 percent of survey respondents include adaptive signal control technology and ramp meters that control vehicle access to freeways.