The usually sensible people at MIT’s Senseable City Lab are looking at the future of the traffic light in the world of the self-driving car, and predict that its days are numbered. Instead, they propose a “slot-based intersections that could replace traditional traffic lights, significantly reducing delays, make traffic patterns more efficient, and lower fuel consumption.”
© Senseable City Lab
It’s based on the principle that if all the self-driving cars are in communication with each other and know where they all are, they can plan speeds and courses so that they essentially pass through each other. It’s very much like air traffic control:
Upon approaching an intersection, a vehicle automatically contacts a traffic management system to request access. Each self-driving vehicle is then assigned an individualized time or “slot” to enter the intersection. Stop and go is largely avoided, which has the effect of reducing pollutants and greenhouse gases caused by acceleration and deceleration cycles.
Untitled from CityLab on Vimeo.
We have seen this movie before, albeit a less sophisticated version, and David Alpert of CityLab was not impressed, writing "But what's missing from this diagram? How about... people?"
The Senseable Lab people say otherwise, suggesting that “slot-based intersections are flexible and can easily accommodate pedestrian and bicycle crossing with vehicular traffic.” But then they note:
“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.”
In fact, in cities you have a lot more than just two flows, you have as many as six or eight when you factor in cyclists, pedestrians, wheelchairs and delivery people riding the wrong way. And as David Alpert noted, people are strange. If the cars are so smart that they know to stop in time to avoid hitting someone, “we might see a small number of people taking advantage of that to cross through traffic, knowing the cars can't kill him. That will slow the cars down, and their drivers will start lobbying for even greater restrictions on pedestrians, like fences preventing midblock crossings.”
I suspect it will be more likely that we get grade-separated walkways like Norman Bel Geddes designed for General Motors in their Futurama at the 1939 World’s Fair, and they have built in downtown Hong Kong.
Dr. Steven Fleming has written about how transportation affects urban form:
The end of the era of private car ownership occasions a genuine rethink of urban mobility and ways in which urban design has historically been used to optimise optimal modes. When trading vessels brought us great riches, we built canal cities like Amsterdam and Venice. When exchanging finance and thoughts was the aim, we built compact cities to shorten walking distances within various quarters, quarters for bankers, quarters for artisans, quarters for tailors, etc.
Lloyd Alter/ Calgary skywalk/CC BY 2.0
The self-driving car will probably cause yet another massive change in urban design; probably it will enable a return to sprawl by making commuting fun, a ticket to Broadacre City. Meanwhile, our cities may turn into Hong Kong or Calgary with pedestrians banned from the streets. Steven Fleming wants us to design our future cities around bikes, but worries that "I’m sure as I write executives from Google are wining and dining politicians, just like Henry Ford, convincing them streets should be given to driverless cars." I suspect he's right. Things to come:
W. H. Corbett 1913/Public Domain