Automotive

Adding just a few self-drive cars to the road gets the traffic flowing

Adding just a few self-drive c...
The self-drive car was tested with 20 human-driven cars on a circular track
The self-drive car was tested with 20 human-driven cars on a circular track
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The self-drive car was tested with 20 human-driven cars on a circular track
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The self-drive car was tested with 20 human-driven cars on a circular track

The next time you're stuck in traffic, take heart because traffic jams may someday be a thing of the past. A team of researchers led by the University of Illinois have discovered that putting only a few self-driving cars on the road can dramatically improve traffic flow. Based on test track results, the teams says that having a mix of only five percent automated vehicles can eliminate stop-and-go waves while producing fuel savings of up to 40 percent.

Traffic jams are an unfortunately all too familiar part of modern life. According to the Texas Traffic Institute, motorists in the United States spend 42 hours a year in tailbacks. There are many reasons for this. Some are obvious, such as too many cars on the road at one time, accidents, poor road design, a steep grade, ring roads designed in the forties but not completed until the eighties, or a city council thinking it's a brilliant idea to stick a convention center over a motorway.

However, there are other, less tangible reasons. There is, for example, the residual traffic jam that can persist for hours after an accident has been cleared away because of having to clear the backlog. Or there's the echo jam that's due to people picking up speed after getting out of a jam only to come up against other motorists down the road, which results in waves of tailbacks even though there are no actual obstacles.

Then there's the simple human nature that takes what should be a theoretically smooth flow of traffic and gums it up. Once the number of cars on a road gets above a certain density, the tendency of drivers to touch their brakes or speed up in a more or less random fashion causes the stream of cars to clump, stop, and start erratically no matter how conscientious the person behind the wheel.

The latter is what happened when the researchers set up an experiment on a test track in Tucson, Arizona. The track was a very simple one. It was circular in shape with one lane, no odd curves, and no changes in grade. When they put 20 or so human drivers on the track and had them drive around, the results were very soon stop and start.

The way in which traffic control experts have tried until now to solve problems like this is by central control. The traffic on selected motorways would be monitored by video cameras or traffic sensors, then the flow would be adjusted by means of traffic warnings by radio, the internet, or texts; variable speed limit signs; opening and closing lanes; or regulating on-ramps.

The problem is that motor traffic is frighteningly complex, and trying to control it in a simple, linear fashion often only makes things worse in a unpredictable ways, so trying to clear a jam in one section may make another one elsewhere that's 10 times as bad.

What the Illinois team is doing is to reverse the solution by using one of the latest trends in traffic monitoring. Where in previous years controllers used cameras to measure traffic flow, today's GPS apps rely on tracking data from drivers' mobile phones. These constantly monitor the phone's position, speed, and direction, and the appropriate algorithms can calculate whether a stretch of road, whether it's a primary artery or a side street, is flowing smoothly or jammed solid.

When applied to an self-driving car, it turns the vehicle, tweaked with a bit of traffic flow theory, control theory, robotics, cyber-physical systems, and transportation engineering, into a "mobile actuator" – a sort of rolling traffic control unit. Essentially, it becomes one of a lot of little controllers handling the problem in its immediate area.

The team found was that by introducing only one autonomous vehicle for every 20 human-driven cars, the self-drive car would soon even out the start-and-stop pattern with a corresponding improvement in fuel efficiency. What surprised the researchers was how simply this worked out.

"Before we carried out these experiments, I did not know how straightforward it could be to positively affect the flow of traffic," says Jonathan Sprinkle of the University of Arizona. "I assumed we would need sophisticated control techniques, but what we showed was that [traffic] controllers which are staples of undergraduate control theory will do the trick."

The team points out that self-driving cars themselves aren't the only solution and that similar technologies, such as adaptive cruise control, can also help to alleviate traffic misery. They also say that while a road system dominated by autonomous cars would be a great improvement, there's still the hurdle of getting through the transition period where a few self-drive cars have to share the road with a large number of unpredictable humans.

"The proper design of autonomous vehicles requires a profound understanding of the reaction of humans to them," says Benjamin Seibold, associate professor of Mathematics at Temple University. "And traffic experiments play a crucial role in understanding this interplay of human and robotic agents."

The Illinois team says that the next step will be to test self-drive cars in denser, more complex traffic scenarios, such as those involving lane changes.

The research was published by Cornell University Library.

The video below shows the self-drive car taming the jam.

Source: University of Illinois

Self-driving cars experiment demonstrates dramatic improvements in traffic flow

9 comments
Eric the Red
WOW, I have been doing this for years. Traffic stopped in front of me, I brake early and leave gaps, try and not to stop. Moving traffic is quicker than stopped traffic. I leave big gaps if there are stopped cars at lights,they turn green and I start to move, rather than waiting for the car in front to move. Not that hard!
FabianLamaestra
@ Eric: I do this too, but in very dense traffic areas the reality is that there is still too many idiots on cell phones, or aggressive drivers that think they're going to get where they're going faster by tailgating, flashing lights/horns, jack rabbit starts, and you just wind up meeting them at the next stop light.
JasonButterworth
I agree. I try to do the same but then your gap runs out when the traffic ahead does not get out of the way in time. I have managed to reduce a half mile tailback that was stopped all together to a 5 mph moving road block. That was cool. The problem with the 20 human drivers here and the vast majority of other human drivers is their tendency to want to get somewhere faster than the traffic will allow which starts off the random braking and stopping scenario. If all drivers could just stay at a constant speed and not panic when the car in front slows just a tad causing them to jump on the brake and reduce their own speed by 50% in a lot of cases then stop start traffic would melt away. Roundabouts are the cause of many traffic jams at busy interchanges given that it takes just one lane on a 4 lane roundabout to block it when hundreds of cars want to get somewhere. The mentality appears to be "I want to get home as quickly as possible and stuff whoever else is on the road. I'm in my own bubble and I am not sharing the road with anybody else!". This leads to 2 or more lanes on a roundabout in heavy traffic to stay stopped for minutes instead of seconds and thereby a complete lack of a bit of give and take regardless of the roundabout rules, a bit of flexibility will allow traffic to flow much more freely from ALL lanes. Autonomous driver-less vehicles would be able to do this without fear of collisions. It is always going to be a human driver who will force evasive reaction from an autonomous vehicle until all human drivers are either removed from behind the wheel en masse or are forced very quickly to live with cars that drive themselves. The drivers that need to leave the road immediately for retraining are those that are scared of driving or cannot reverse their own cars without mounting a curb or crossing the entire road in the process. Those always make me laugh. When they can retrofit AI and autonomous driving into ANY car the industry should then work with government to make it a mandatory required change. It would help reduce carbon and other emissions within a very short time and it would reduce accidents just as quickly. Rant over! :D
owlbeyou
Well of course the traffic will run more smoothly if you drop in a self-driving car. It's like a game of follow the leader, except the leader is driving steady and s-l-o-w-e-r. Those pressed for time will get even more frustrated and prone to mishaps. This study isn't as useful because in its attempt to find a solution, it creates another problem. There will always be drivers who want to drive faster, so keep autonomous cars in the slow lane please. The only advantage I can think of at the moment is self-driving cars won't be slowing down to rubberneck other accidents on the way.
DavidIngram
Reality is going to bite this plan in the posterior. Autonomous cars in a mix will give us another "lowest common denominator" and thus gridlock.
Douglas Bennett Rogers
Just need an external input for the cruise control that engages at a set traffic density.
Captain Obvious
Some of you people get it, some of you people ARE the problem. I try to drive just like the autonomous car, and usually successfully smooth out the flow but sometimes the jerks just go around me and slam on their brakes ahead of me. As George Carlin said, "You know how dumb the average person is? Well, half of the people are dumber than THAT."
SteveO
This result based on the experiment design should not have been unexpected. Try doing the same experiment with 2 lanes and see what happens. I would bet the ratio of self-driving to human driving will need to be flipped.
Tanstar
As Cap Obvious pointed out, you can leave bubbles in front of you (this is safer too), but then an aggressive driver will just cut in front of you, forcing you to slowdown more to create a gap, leading to another aggressive driver to cut you off . . .