After more than a century with the classic red, yellow and green colors, Roman traffic lights could gain a fourth color. It will be white, and will not be useful to real motorists.
The topic was officially introduced in the capital by Luigi Di Matteo, head of the technical area of the ACI, who spoke on the portal of Roma Servizi per la Mobilità, the Roma Capitale agency that manages the entire city traffic light network. The white, explained Di Matteo, would serve to indicate that the intersection is mainly managed by autonomous vehicles and digital coordination systems, therefore we would have connected vehicles capable of communicating with each other and with the infrastructure, a case which would automatically optimize the passage. For motorists, the meaning would be simple: follow the flow of the vehicle in front, while the system coordinates the overall movements.
Where did the idea come from?
The origins of the proposal are academic and date back to 2023, when a group of researchers from North Carolina State University published in the journal IEEE Transactions on Intelligent Transportation Systems the study White Phase Intersection Control Through Distributed Coordination: A Mobile Controller Paradigm in a Mixed Traffic Stream which starts the international debate. The concept, called “white phase”, is based on a distributed computing principle: each autonomous vehicle approaching the intersection contributes its computational capacity to coordinate traffic in real time, communicating with other vehicles and with the traffic light itself.
The numbers from the simulations are important: even with only 10% of autonomous vehicles at the intersection, waiting times would be reduced by 3%, a percentage that would rise to 10.7% when and if autonomous vehicles reached 30%. Within a scenario with a high concentration of driverless cars, some studies speak of reductions of up to 90% in delays.
How it works for drivers
The logic is simple. When enough autonomous vehicles approach the intersection, the white light is activated, signaling that the cars are coordinating their movements to facilitate flow. Human drivers would not have to do anything special, as red, yellow and green would remain the usual references. When the light turns on, it would be enough to adapt to the flow, and if autonomous vehicles were to be few, if not completely absent, the traffic light would return to the classic sequence.
The Roman traffic light network today has 1,458 systems, of which 793 are centralized on the main access arteries to the city. Roma Servizi per la Mobilità has already delivered the project for the installation of 630 new systems with countdown device to the Capitoline Department, with the start of installations expected in the second half of 2026.
The Municipality’s about-face: no experimentation in sight
However, the councilor for Mobility of Rome Capital, Eugenio Patanè, intervened on the topic and dotted the i’s. The possibility of seeing traffic lights in Rome with a fourth white light for self-driving cars “is fake news to be totally denied, not true: there is no experimentation”, statements reported by Adnkronos. The distinction is relevant, because what is described by Roma Servizi per la Mobilità and the ACI is a study scenario on the future of mobility, not an operational project already in the pipeline.
In short, the fourth light exists for now only in simulations – and in the direction in which urban mobility could go in the coming decades – and it is worth specifying that no experimental project exists, at least in the short term.
