Smarter Traffic Solutions–But Will They Work in the City?

Oct 06 2010 Published by under [Science in Society], Transit

Hey, Drivers, is there a traffic light you know you have to make? You know the one--it takes ages for the light to change from red to green, and the green light is only what feels like a few seconds long. Well, what if there was a smarter traffic light? What if it could sense the traffic flow, and change to match the volume of cars on the road? According to ScienceNews, researchers from the Santa Fe Institute are working on just this particular solution (see original working paper here.) It sounds like the end of road rage, but will it work in New York City?

The original paper notes that classic traffic light control strategies are rather limiting: They aren't very flexible in terms of adapting to traffic conditions. In fact, their adherence to rigid time codes often result in delays for all motorists:

Due to stochastic fluctuations, even optimized green times are usually either too short (creating multiple red lights for queued vehicles that could not be served) or too long (creating unnecessary delays to vehicles of other ow directions) (2).

Instead researchers are propose traffic responsive systems that can not only adapt to traffic conditions but communicate locally to increase flow. So not only can the light sense an increased volume of cars on the road, but it can tell the next light that those cars are coming, which will then tell the next light and so on to keep the flow of traffic moving--achieving the much sought after "green wave."

The green wave is the occurrence of sequential green lights along a route, allowing groups of vehicles to move continually--generally reducing travel time, increasing fuel efficiency, and minimizing overall incidences of fist shaking. (Okay, okay. I'm being snarky. I don't know that people actually shook their fists less, but less traffic should make everyone happier, no?) Currently, the green wave is managed. That is, the cycle is controlled and deployed during rush hour and other times of perceived peak time. But this system cannot account for variability--it does not know how many cars are waiting at a light, it does not know which direction the cars are traveling in, and it does not know where cars are turning to create new hubs of congestion.

The new system would.

How does it work?

[The] arrangement puts two sensors at each intersection: One measures incoming flow and one measures outgoing flow. Lights are coordinated with every neighboring light, such that one light alerts the next, “Hey, heavy load coming through.”

That short-term anticipation gives lights at the next intersection enough time to prepare for the incoming platoon of vehicles, says Helbing. The whole point is to avoid stopping an incoming platoon. “It works surprisingly well,” he says. Gaps between platoons are opportunities to serve flows in other directions, and this local coordination naturally spreads throughout the system.

It's been tested in Dresden, which has 3 traffic light–controlled intersections, 68 pedestrian crossings, a train station that serving more than 13,000 passengers daily, and seven bus and tram lines that that complete a unidirectional run every 10 minutes. The results were impressive: "The flexible self-control approach reduced time stuck waiting in traffic by 56 percent for trams and buses, 9 percent for cars and trucks, and 36 percent for pedestrians crossing intersections." And Dresden is on board with adopting the system.

My last really bad encounter with New York City traffic happened in June. The hubby (S) and I had a trip planned to North Carolina. He was supposed to pick me up in lower Manhattan, and we were supposed to take a tunnel out of the city. Easy. Nope. It was a gridlock day. We spend an hour sitting in the same spot. The reason: whichever group had the green light would flow into the intersection whether or not it was clear and they could fit. The result was that no one got very far. I have very artfully recreated this event for your visual pleasure:

Yes, it's a mess. That's exactly what it is meant to convey. The arrows indicate the direction of traffic and the circles are meant to demonstrate the number of cars from that particular direction that actually made it through the intersection. (We were in the blue group.)

My point is that this sensitive, flexible system sounds great, but how does it account for the humans behind the wheel who push their way through? What are your thoughts?



Lammer, Stefan and Dirk Helbing. (2010) Self-Stabilizing Decentralized Signal Control of Realistic, Saturated Network Traffic. Santa Fe Institute.

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