Can Smarter Red Lights Let Cars Drive Greener And Save Gas?

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Traffic light

Traffic light

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We've all driven through--or waited a long time at--intersections that have car-sensing traffic lights.

Now Denso has modeled the next iterations of a "smart traffic light" system. It would use messaging between vehicles and the traffic-light controller to let the light make better decisions about when to change, to maximize overall vehicle throughput.

And that, in turn would reduce the number of minutes cars spent idling at traffic lights, cutting their emissions and their fuel usage.

In other words, cutting red-light time helps you go green.

Traffic light, meet oncoming car

Today's car-sensing lights stay green in one direction until a car wants to enter the intersection from the cross street, when the light is directed to change based on sensor data from a loop of wire in the roadway.

Denso's proposed system uses short-range wireless transmitters (think your WiFi router) in cars and elements of the road infrastructure. The field is broadly known as V2V (for vehicle to vehicle) communications.

Speed, density, and type of vehicles

Traffic lights that "knew" more about upcoming vehicles could change dynamically based on their approach speeds, the mix of vehicle types (e.g. compact car, tractor-trailer truck), and the relative volumes of cars approaching from any direction.

This would let a stoplight "know" that one single vehicle was approaching from a given direction, and delay a regularly scheduled change long enough to let it pass through.

Smart intersection components, from Denso Corp.

Smart intersection components, from Denso Corp.

Enlarge Photo

Two tractor-trailers traveling one after the other could signal their presence to the light, allowing it to stay green in one direction long enough to let the pair (which together extend the length of five or six cars) pass through.

Data on whether a car was accelerating, braking, or flashing a turn signal would all factor into signal timing--including the duration of optional features like turning-lane arrows.

Optimum flow

Some express city transit buses already carry equipment that lets them pre-empt changing traffic signals, to reduce time lost waiting at red lights. The theory is that a bus with 50 passengers can and should take priority over 20 single-occupant cars.

Denso's model, however, goes well beyond the current signal-control algorithms--which use averages of traffic flow--to adjust cycle times and light extensions to get to the "state optimum" for any given set of upcoming vehicles.

The company has been testing both pre-empting red lights and extending green lights via transmitters onboard the vehicle and receivers in stoplights at its Vista, California, research facility.

Motorcycles, even bikes?

Ultimately, not only vehicles but motorcycles and perhaps even bicycles might carry signaling transmitters to take their place in the data flow.

Since engine idling at stoplights produces gas mileage of 0 mpg, and accelerating up to speed uses far more fuel than maintaining a steady speed, the savings come not only in time but also in reduced fuel usage and lower emissions.

How would you feel about a transmitter on your car that "talked to traffic lights"? After all, on this one there's a clear payback: Without such a transmitter, the stoplight couldn't stay green to let you through because it wouldn't know you're approaching.

Give us your thoughts in the Comments below.

[SAE Automotive Engineering]

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