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.

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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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Comments (8)
  1. Love the idea! Location based service apps on phones are already tracking everything we do, might as well add this to the list.

  2. Can't wait to see what the hotrodders do to convince traffic lights to give them clear sailing regardless of oncoming cars and trucks...

  3. Where is the hybrid love man. We don't use gasoline when idling.
    Actually I love this idea. I have seen how much better a traffic cop can be compared to a dumb light. Smarter signals would be great.
    But can they use it to stop gridlocked intersections? That would save even more gas.

  4. I'm predicting this will go down as one of those "Duh! Why didn't we think of this before!" examples.

  5. a big gripe of mine is how our traffic signals work now, as opposed to how they used to work. my area, of course. i dont know how they work in other areas.
    it used to be that you could time lights. if you drove on busy streets, the lights would stay green for longer periods of time. and there was way less starting and stopping. it does not take much fuel to idle. it takes a whole bunch to restart the car from rest.
    now in my area, the lights (especially at night) go on and off, on and off. one car, coming from a low use street, will almost immediately make it green for him, while 10 cars on the opposing busy street, who would all have made the light within reason, are all forced to decelerate, and possibly come to a full stop.
    there is way too much attention on the vehicle that is stopped. poor fellow may have to wait 30 seconds. his whole day will be ruined !!!! once you are stopped, you are stopped. it wastes very little fuel to idle. probably even less with an ev.

  6. one big thing i would do is have the yellow light last much longer (15 seconds or more). this would give a driver much better knowledge if he can make the green light from a fairly long distance away.
    if he knows he cant make it, he can just place the car in idle, and coast towards the light, wasting very little fuel. hopefully never having to come to a complete stop, such that the car may slow down to 10-15 mph, instead of a complete stop. it takes a lot of fuel to overcome the inertia of a stopped vehicle.
    of course, it also requires a lot of people to change their mindset, and not be so ridiculous on the road.
    i see people accelerate past me or some other vehicle, when the light in front of them is red. i mean talk about STUPID. yet i see it time and again. in a heavily populated area like mine, there are stop lights every several hundred feet sometimes. combine the number of stoplights and the way they work, and you constantly have vehicles driving 40 miles an hour coming to a complete stop in a few seconds. a tremendously big waste of fuel.

  7. I'd prefer my car not have a transmitter to talk to an upcoming light. In my home town, nobody bothered to adjust the traffic lights so timing the lights isn't possible. That's a simple fix that the Department of Transportation should and could require all localities to implement. With that minor adjustment, it can control the flow, and to some extent, the speed of traffic. For people who accelerate rapidly from one light to the next, let them wait. The signals, timed or not, also break up the flow of traffic so there are occasional gaps, allowing vehicles from non-traffic-light-controlled intersections to enter the controlled street far more easily with less of a traffic hazard to all.

  8. I made a short survey to see if people like the V2V idea. Click here to express your opinion ....

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