The White Traffic Light is Coming: What it is, How it Works, and Why it Will Change the Way We Drive in Cities

We are used to stopping at red, slowing down at yellow, and going at green. But soon a fourth light may be added to urban traffic lights: white. This is not science fiction or a marketing gimmick, but a real scientific proposal, born in academia and increasingly taken seriously in Italy.

The idea was developed by a team of researchers from North Carolina State University, led by Professor Ali Hajbabaie from the Department of Civil Engineering, and published in the peer-reviewed scientific journal IEEE Transactions on Intelligent Transportation Systems. The study, whose first version dates back to 2023, proposes adding a white light to traffic signals to intelligently manage intersections in the era of autonomous vehicles: when a sufficient number of connected cars are near an intersection, the white light turns on, the vehicles communicate with each other and with the infrastructure, and the flow is automatically optimized without the need for fixed red-green cycles.

For human drivers, the meaning of the white light would be immediate and intuitive: follow the vehicle in front and let the system do the rest. Simulations conducted by the NC State team produced remarkable results: in scenarios with a high penetration of autonomous vehicles, traffic delays could be reduced by up to 94%. Even with a modest percentage of just 10% of autonomous cars on the road, waiting times would still decrease by 3%, with direct benefits on consumption and emissions. In 2024, the same university published an update to the study that extends the model to pedestrians as well.

In Italy, the debate has officially reached Rome. Roma Mobilità, the municipal company that manages the city's traffic light network, recently published an in-depth analysis on the topic, featuring statements from Luigi Di Matteo, head of the Technical Area of ACI, who illustrated the potential of the white traffic light in the context of smart roads. Currently, this is a phase of study and evaluation, not yet an approved operational plan: no municipal resolution, no call for tenders. But the fact that Roma Mobilità and ACI are publicly discussing implementation is already a significant sign of the direction in which Italian urban mobility is moving.

The main issue, common to all of Europe, remains the critical mass of autonomous vehicles necessary for the system to really work. With the number of connected vehicles currently on Italian roads still negligible, the white traffic light is destined to remain an experimental hypothesis in the short term. However, in the long term, the picture changes: the European Union aims for a significant penetration of assisted driving vehicles by 2030, and infrastructures like the one proposed by NC State could become the standard for next-generation smart cities. Rome, with its chronic traffic problems, would have every interest in being among the first to adopt it.