Automotive

Study shows tailgating can slow everyone down

Study shows tailgating can slo...
A study by MIT researchers has found that maintaining equal distances between the car in front and the vehicle behind can help improve traffic flow
A study by MIT researchers has found that maintaining equal distances between the car in front and the vehicle behind can help improve traffic flow
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The study’s authors say that if drivers kept an even distance between cars rather than tailgating in an attempt to push ahead, traffic flow would remain even
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The study’s authors say that if drivers kept an even distance between cars rather than tailgating in an attempt to push ahead, traffic flow would remain even
MIT professor Berthold Horn (left) and postdoctoral associate Liang Wang, co-authors of the new MIT study
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MIT professor Berthold Horn (left) and postdoctoral associate Liang Wang, co-authors of the new MIT study
A study by MIT researchers has found that maintaining equal distances between the car in front and the vehicle behind can help improve traffic flow
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A study by MIT researchers has found that maintaining equal distances between the car in front and the vehicle behind can help improve traffic flow
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When unexplained traffic jams happen, says an MIT Computer Science and Artificial Intelligence Laboratory (CSAIL) study, you can probably blame tailgaters. The researchers say that if drivers kept an even distance between cars rather than driving too close to the vehicle in front, traffic flow would remain even. This "bilateral control," could double the speed of the average vehicle on busy highways.

"We humans tend to view the world in terms of what's ahead of us, both literally and conceptually, so it might seem counter-intuitive to look backwards," says MIT professor Berthold Horn, co-author of the article. "But driving like this could have a dramatic effect in reducing travel time and fuel consumption without having to build more roads or make other changes to infrastructure."

According to MIT, the average urban commuter in the US spends 38 hours per year stuck in traffic, wasting 19 gallons (72 liters) of fuel. The costs of traffic congestion in the US are estimated to be $121 billion per year, or $820 per commuter, and use a total of 2.9 billion gallons (11 billion liters) of fuel. This does not include accidents caused by traffic disruptions.

The CSAIL study, published in the journal IEEE Transactions on Intelligent Transportation Systems, concedes that changing driver behavior would be a long, not very rewarding process. But what could change with relative ease is how adaptive cruise control systems found in most cars operate.

Adding rear radar sensors to a car with adaptive cruise could allow the vehicle to work to mediate its average distance between other vehicles, both ahead and behind. If just a few vehicles were outfitted and working this way, Horn says, the improvements to traffic flow would be immense.

The mathematics behind the idea are simple and can be likened to a vehicle's shock absorption system. When springs are placed between cars, as they are between the wheel and the vehicle's chassis, they flex and extend to continually maintain an equilateral distance between the vehicle and the wheel as a self-contained system. The CSAIL proposal is similar with a vehicle in question, using adaptive cruise control, maintaining equal distances between the car in front and the one behind through speed adjustments.

This ideal is very different from what is the norm in most thinking about traffic, especially by those stuck in it. Drivers (and, consequently, vehicle control systems) tend to be looking ever forward, responding only to what's ahead and largely ignoring what's behind. Thus, in stop-and-go or slow-and-go situations (traffic jams), each vehicle reacts to the vehicle in front, causing intermittent slowdowns or stops (jams) in wave-like patterns. When vehicles are working to maintain equal distances both from the car in front and the vehicle behind, the MIT paper contends, these wave patterns are minimized and traffic flows more smoothly.

And thanks to funding from Toyota and others, Horn is looking to undertake simulation testing in the future to determine if his method is indeed both faster and safer for drivers.

This latest study follows on from a more limited study of bilateral control conducted by Horn and published by IEEE in 2013. Another study by an electrical engineer, William J. Beaty, noted traffic patterns he called "Traffic Waves," outlined in a paper in 1998. Other traffic theories have been proposed, many based on fluid mathematics. The National Science Foundation has granted collaborative research, often based at MIT, on these studies.

More research has confirmed other traffic-busting ideas such as lane splitting for motorcycles and how artificial intelligence systems and self-driving vehicles could cope.

What's different about this latest study from MIT's CSAIL is its focus on solutions. Looking at both the micro- and macro-mechanics of traffic flow, Horn and Wang have proposed a relatively simple answer that can be applied using current technology.

Adding rear-facing radar to adaptive cruise control and programming the vehicle to maintain equal distances front and back, when possible, would go a long way towards resolving many tailgating-caused traffic jams. Even if, the researchers contend, only a relatively small percentage of vehicles on the road are using this technology adaptation.

Source: MIT CSAIL

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12 comments
VincentWolf
" and use a total of 2.9 billion gallons (11 billion liters) of fuel. "
Lost in all this nonsense is that if you drive an EV powered by the sun and sit in traffic even all day your not burning up fuel that's producing the pollution from burning up those extra 2.9 billion gallons of fossil fuel.
People driving gas cars when alternatives are available are the scum of the Earth in my opinion.
Rusty Harris
I know it slows me down, because when someone tailgates me, I just back off the gas pedal. If they are in THAT much of a hurry (I typically drive between the speed limit & 7mph over), they can go around me.
aksdad
And another reason why tailgating is a bad idea. Never mind that it’s illegal and dangerous.
Static
Bit harsh Vincent, people cant afford the ridiculously expensive e cars....
Plus, didn't need MIT to figure that out, worked that out 40 years ago...
Miner Bob
When I drive in traffic I can tell who's following too close by the many times they step on their brakes. Best thing is to back off and make a game out of spacing yourself so that by time you come up on them they're moving again and you never touched your brakes.
You're not going to get past the traffic so it's best to just cruise along at 20-30mph instead of acting like the idiots that zoom up on the cars ahead and stand still for 2 minutes and then start moving.
Riaanh
Bob you are right, I judge the driving skills of people by how often they use their brakes on the freeway. Everytime you touch your brakes you are wasting momentum, for which you need fuel to regain it again.
Deres
I think this analysis does not take into account all parameters. It may be true before the jam. But Inside the jam, the effect of people wanting to change lane all the time to gain time is not negligible. In fact, if everyone was letting more space, aggressive drivers would change lane everytime their lane is moving slower. This would quickly neutralize all movement in the start of the jam. Moreover, in the case of an entry on the highway, this could block the highway.
MarylandUSA
I'm fairly sure this phenomenon was pointed out in 2008 in the book Traffic: Why We Drive the Way We Do by traffic engineer Tom Vanderbilt ( http://a.co/iERFzip ).
MarylandUSA
I agree with Scottsdale Bob that rational drivers seldom apply their brakes. As soon as that distant traffic light turns yellow, I turn off the cruise control and coast to the finish line, alternately coasting and low-gearing my 6-speed automatic. My 2011 Fiesta has gone 113,000 miles, and I've never had to replace the brakes' front discs or rear shoes.
Jeff Goldstein
Study is wrong. It makes too many assumptions. Traffic actually tends to bunch up in back of a few slow drivers. People tailgate to try to get around these drivers who are obstructing traffic. The best way to speed up traffic flow and decrease congestion is to enforce the laws to keep to the right except to pass and to set speed limits using the 85 percentile rule instead of politics.