Traffic Intersections Without Traffic Lights But More Efficient Flows

Traffic jams around intersections are a thing of the past, in theory. The mathematical based model possibly enables to replace traditional traffic lights and makes traffic patterns more efficient.

In many cities, traffic intersections with traffic lights are often placed relatively close to each other. It slows down traffic flows. This in turn means more traffic noises, emissions, traveling times, and frustrated road users. A slot-based intersection, developed by an international group of researchers at the Massachusetts Institute of Technology (MIT), the Swiss Institute of Technology (ETHZ), and the Italian National Research Council (CNR), can make a substantial contribution to fluent traffic flows. In order to reduce delays and fuel consumptions, the mathematical based model enables to replace traditional traffic lights and makes traffic patterns more efficient. The published study “Revisiting Street Intersections Using Slot-Based Systems” presents the results.

Throughput of Traffic Intersections Reduced by Highly Sub-Optimal Conditions Caused by Traffic Lights

“Traffic intersections are particularly complex spaces, because you have two flows of traffic competing for the same piece of real estate,” says Professor Carlo Ratti, Director of the MIT Senseable City Lab, which initiated the study. “But a slot-based system moves the focus from the traffic flow level to the vehicle level. Ultimately, it’s a much more efficient system, because vehicles will get to an intersection exactly when there is a slot available to them.”

The phased switching process of traffic lights is normally working periodical. Only a number of non-conflicting flows can pass the intersection at the same time. Immediate phase transitions are generally impossible. The transition between phases is realized by a setup phase (amber light) and takes five to eight seconds. This highly sub-optimal conditions slow down traffic flows and cause congestions. The more frequent, the more setup phases and less intersection throughput.

The newly published study co-authored by MIT researchers claims this kind of traffic-light-free transportation design, if it ever arrives, could allow twice as much traffic to use the roads. An essential component of the scenario are sensor-laden, self-driving vehicles. Upon approaching an intersection, vehicles communicate with a traffic management system to request access. Then, an individualized time or “slot” is assigned to each self-driving vehicle to enter the intersection. Stop-and-go traffic can be reduced to a large extent. The largely avoided acceleration and deceleration cycles mean less pollutants and greenhouse gases around traffic intersections. All vehicles remain at a safe distance to each other while they pass the junction. Slot-based intersections can easily include pedestrians and bicycles.

“It is important that we start looking into the impact of self-driving vehicles at the city level as soon as possible,” added Ratti. “The lifetime of today’s road infrastructure is many decades and it will certainly be impacted by the mobility disruptions brought in by new technologies.”

Via MIT News, Senseable City Lab, Plos