Researchers at MIT, ETHZ, and CNR have developed slot-based intersections that are more efficient than traffic lights, eliminating queues and delays.
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) have developed slot-based intersections that could replace traditional traffic lights, significantly reducing queues and delays. Results of the study will be published in the journal, PLoS ONE on March 16, 2016 (Full article details: "Revisiting Street Intersections using Slot-Based Systems”, by Remi Tachet, Paolo Santi, Stanislav Sobolevsky, Luis Reyes-Castro, Emilio Frazzoli, Dirk Helbing, Carlo Ratti).
The idea is based on a scenario where sensor-laden, self-driving vehicles pass through intersections by communicating and remaining at a safe distance from each other, rather than grinding to a halt at traffic lights. By removing the waits caused by traffic lights, slot-based intersections speed up traffic flow.
“An intersection is a difficult place, because you have two flows competing for the same piece of real estate,” says Professor Carlo Ratti, SMART Future Urban Mobility Interdisciplinary Research Group (FM IRG) Principal Investigator and Director of the MIT Senseable City Lab where the study was initiated. But a slot-based system and no traffic lights, he adds, “moves control from the traffic flow level to the vehicle level. By doing that, you can create a system that is much more efficient, because then you can make sure the vehicles get to the intersection exactly when they have a slot.”
Slot-based intersections are similar to slot-based management systems used for air-traffic control. Individual self-driving vehicles are granted personalized “slots”, thus eliminating the need for stopping (as it happens with current traffic lights). “Transitioning from traffic light to slot-based system could dramatically improve intersection performance, with traffic volume queues vanishing and travel delays cut to almost zero”, added Paolo Santi, a Research Scientist at the MIT Senseable City Lab and member of the Italian National Research Council.
In particular, results show that intersections providing real-time slot allocation might double the number of vehicles an intersection with traffic lights can manage. Such effect, in turn, would have a major impact on the whole road network of a given city. "Travel and waiting times would be considerably reduced and fuel consumption would go down”, said Professor Dirk Helbing of the ETHZ. “This would make a contribution to the reduction of emissions and climate change. Overall, people would benefit, the environment would benefit, and cities would become more livable."
Another feature of slot-based intersections is that vehicle speed is controlled so that each self-driving vehicle reaches the intersection in synch with the assigned slot – so that stop and go is avoided. The latter, in turn, results in reduced emission of pollutants and greenhouse gases caused by acceleration and deceleration cycles. Furthermore, slot-based intersections are flexible and can easily accommodate pedestrian and bicycle crossing with vehicular traffic.
“It is important that we start looking into the impact of self-driving vehicles at the city level as soon as possible“, adds Ratti, who is also one of the 17 members on Singapore’s Committee on Autonomous Road Transport for Singapore (CARTS).“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.”
The research team was led by Paolo Santi and included Remi Tachet, Stanislav Sobolevsky and Carlo Ratti at the MIT Senseable City Lab, Emilio Frazzoli and Luis Reyes-Castro at the MIT Laboratory for Information and Decision Systems, and Dirk Helbing at the Swiss Institute of Technology. Research activities have been supported by ENEL Foundation and the Singapore-MIT Alliance for Research and Technology (SMART).
ADDITIONAL MATERIAL. A video showing a side-by-side comparison of slot-based and traffic light intersections can be downloaded at http://senseable.mit.edu/light-traffic/
The article: "Revisiting Street Intersections using Slot-Based Systems”, PloS ONE, 2016, by Remi Tachet, Paolo Santi, Stan Sobolevsky, Luis Reyes-Castro, Emilio Frazzoli, Dirk Helbing, Carlo Ratti can be accessed on the journal PLoS ONE website.
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Started in 2005, the Senseable City Lab at the Massachusetts Institute of Technology a multidisciplinary research group that studies the interface between cities, people, and technologies. It investigates how the ubiquity of digital devices and the various telecommunication networks that augment our cities are impacting urban living. With an overall goal of anticipating future trends, the Lab bring together researchers from many academic disciplines to work on groundbreaking ideas and innovative real-world demonstrations. This research is undertaken in partnership with cities, the private sector and other universities; through this collaborative approach we strive to reveal how a new, rapidly expanding network of digital devices is serving to modify the traditional principles of understanding, describing and inhabiting cities. The Lab's work has been exhibited in leading venues including the Venice Biennale, the Design Museum Barcelona, the Canadian Centre for Architecture and MoMA The Museum of Modern Art In New York. Among many awards are TIME Magazine's Best Invention of the Year in 2007 (Digital water Pavilion) and 2014 (Copenhagen Wheel).