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“Platooning” Reduces Drag and Cuts Fuel Consumption and Emissions

An automated way of allowing cars to drive much closer to each other in heavy moving traffic—“platooning”—could cut congestion and reduce fuel consumption and emissions by reducing aerodynamic drag, according to researchers from Jadavpur University in Kolkata, India. Their work is described in a paper in the current issue of the International Journal of the Environment and Pollution.

Traffic congestion is a growing problem across the globe and is becoming acute in areas of rapid economic growth, such as China and India. Congestion exacerbates the already growing problems of rising fuel consumption and emissions of criteria pollutants and greenhouse gases.

Automated highway systems are one of the approaches being explored to mitigate congestion, and platooning—the synchronized movement of two or more vehicles as a unit, travelling at the same speed with relatively small inter-vehicle spacing—is one of the possible aspects of such an automated system.

Debojyoti Mitra and Asis Mazumdar at Jadavpur University assessed drag on a maximum four-vehicle platoon model inside the university’s wind tunnel using several car and bus models as platoon members. Intra-platoon spacing was 2/5th the length of the vehicle—e.g., cars 5m in length were spaced 2m apart. Air velocity was 23 m/sec (82.8 km/h or 51 mph).

They found that the platooning of vehicles at close spacing reduces the drag coefficients of all platoon members, regardless of the vehicle’s shape. The higher the number of vehicles in the platoon, the lower the drag coefficient.

The leading car in the platoon experiences the highest drag as you would expect but no more than if it were driving alone. The second car has a much lower drag coefficient than the first car in a two-car platoon. The middle car experiences the lowest drag in a three-car platoon and the third car in the platoon, starting from the front, experiences the least drag in a four-car platoon.

—Debojyoti Mitra
Drag coefficients (CD) in a four-vehicle platoon
  Car platoon Bus platoon
Vehicle 1 0.331 0.868
Vehicle 2 0.273 0.602
Vehicle 3 0.225 0.424
Vehicle 4 0.284 0.521

To make such an approach practical from a safety point of view, sensors and safety controls that allow vehicles to drive at such a small separation would be required.


  • Mitra, D. and Mazumdar, A. (2007) ‘Pollution control by reduction of drag on cars and buses through platooning’, Int. J. Environment and Pollution, Vol. 30, No. 1, pp. 90–96.



Didn't I see this in the 90's on "Beyond 2000"? Yes, I did. In CA, they have a long stretch of highway with sensors to test this kind of system. Wow, these guys are talking like they discovered this. Whatever, seems like it's not going to happen anytime soon.


Yes I saw it on Beyond 2000 as well. They had radar sensor set up and monitored the distance automatically. It was pretty cool, although I wouldn't expect it to work without much coordination of sensors etc. What would happen if the middle car needed to exit unexpectedly? Would override be allowed? Interesting though.


This idea is for the birds - they invented it and that's where it should stay. Just wait until the Microsoft Windows controlled system goes down with hundreds of cars 2m apart at 50mph. Horrific. What is so difficult about just making cars like the Prius with a Cd of 0.26?



Well, the Hypermilers swear by this stuff. The safer way to do it is to follow a big rig at less than 5 car lengths. They have a a bigger lower pressure plume behind them, and they usually go slower, so you use less fuel that way too, if you're at the bottom RPMs of your highest gear. I think you guys are right though...many problems with making this routine.


it took these guys how long to figure this out? nascar has known about it for years...it's called drafting.

i have a better idea to reduce congestion - fewer cars.


This is old news!! In NJ we call this tail-gating.


Ric Romero wants his tag back!

With AI auto-pilot this will become practical but with human tailgaters this will be a nightmare!

Robert Schwartz

We got us a convoy!


Robert: re convoy: LOL, land sakes alive, are you showing your age!

Stan Peterson

This is a description of 21st century new mass transit. It has the ability to remove the last vestiges of the antique mass transit that no one wants to use, any longer than absolutely necessary.

Such a mass transit system will truly take you from Point A (where you are) to Point B (where you want to go).

Current antique mass transit does not do that. It makes you go to another place near where you are (Point A') to (Point B') near where you want to go. Further it only allows you to do that at certain hours and frequencies. Having watched Manhattan business absolutely stop because businessmen must absolutely catch the train home. There are people that can't take the mass transit to the ballpark, because the train doesn't run by the time a night game ends. Ditto for a night out on the town.

And it is coming much sooner than many of you think.

The necessary pieces are being adapted and showing up in cars. For example high priced vehicles already have "intelligent cruise control" that maintain spacing between cars. This option will spread to cheaper and cheaper cars over time.

The NHTSA has established 2012 as the year when all vehicles will be required to have stability control. This would also include ABS as well as automated way to apply the brakes to prevent skids and rollovers.

Add to that the GPS navigation system becoming more common already and not just a luxury car option, and it is not hard at all to envision a distributed system with little centralized control needed to create "trains of closely spaced cars".

Modern wireless internet access would provide the infrequently needed central advisories. Local Wifi would allow communication between adjoining cars in the trains to communicate between adjoining cars joining or leaving automated close spacing mode.

Furthermore the new mass transit has the option (eventually!) for unmanned driving. Rather than take you to a parking lot near where you want to be, it could drop you at the front door. It could return to pick you up on schedule or if summoned, when a change of plan occurs.

Just like a chauffeur driven limousine. And that is what people would want from a "modern mass transit" system. Privacy, independence in destination, and time of leaving or arriving.

It will happen at first in the multi-passenger "diamond lanes" of freeways. I could certainly see the first such attempts by the mid-teens, and quite common by 2030.


Trains anyone? Why not attach a hitch on each car so they can all hook up to each other. Wait a minute! They're called trains! I still can't understand why N.America started removing trains and tracks while Europe (yay for them) started putting them in. I think they've got something there.

Australia has something called truck trains, each truck carries a load of 8 or so trailers. Seems logical to me. Break the train up into 8 seperate trucks and your wasting fuel on the extra drag produced by each of the other 7 trucks (obviously less efficient). I say get rid of trucks all together and use trains, that way we could free up the congestion on our highways too!

Seems to me we have to get away from the "I want it now syndrome". Retailers can get products in, in less than 2 days. If we switched back to rail, consumers won't buy so much useless stuff. It'll even help reduce global warming.



"Just wait until the Microsoft Windows controlled system goes down..."

How do you know the operating system isn't a MAC or Linux? Did you make an assumption?


Yes, it can be done. The computing and sensors are good enough.

Should it be done? Probably not now. The delays in waiting for the convoy to form and the problems when drivers change their minds about exiting, etc. might be formidable.

Not all vehicles can accelerate and brake at the same rates and not every one will meet its own design specs.

For large trucks on long hauls it might be much more practical. And a good place to try first. In Australia I understand that a run of 500 miles w/o encountering traffic or dealing with exits is not unusual.


This is ridiculous. It's common knowledge as stated already, all forms of racing, bicycles, cars, skis, running have exploited the benefits of "drafting" or "slipstreaming" since the dawn of motion. And just as in NJ, MA is the same way, I'm about to head out into a 400 car "platoon" right now, so if I'm 399th, does that make my Cd 0.0?

(just kidding about the last question by the way, a fecetious extrapolation of this groundbreaking data)


I'm not certain drag reduction is going to have much near term impact if it requires 2M spacing. The increased vehicle throughput smart cruise control offers could dramically reduce congestions and drivetimes with as few as 20% of the vehicles on the road using it. Transporation departments might do well to require the use of this type of technology as a less expensive option to adding additional vehicle lanes.

Bill Young

If you really want to save gas, set up a 25 car convoy with 1/2 car length spacing. Take the convoy to about 60mph. Then the lead car slams on the brakes. Viola! we have 25 less cars on the highway.


This sounds very hi-tech. While I am not against hi-tech, surely it would be easier just to introduce smaller cars! (I recommend the Smart Car!)

Michael McMillan

This is not limited to a single stream of cars. a pair of vehicles side by side also get a significant decrease in resistance.

For the best patterns, look to bike racers. As a bike racer, you can feel in drag as the air buffets against your skin which lets you more quickly find an optimal shape.

If there are two riders, they ride single file, same for up to about 4 or 5 riders. At 6 riders, side by side riding feels fairly efficient, ie two single rows of 3 riders riding side by side. The double header also reduces the amount of power needed by the front rider to maintain the same speed. That works for up to about 10 riders. At 10 riders, the shape starts to change to a somewhat diamond shape where more riders attempt to remain at the point in the shape where there is the least air resistance.

For a large field of several hundred riders, you end up with a sort of diamond shape.

-Michael McMillan


Some people seem to have mis-conception about how this thing would work. Its not to simple but if/when cars have autopilot (if only on the highway) two or more cars could "talk" to each other over wireless and orchestrate their movements in unison. This means that if the front car brakes all cars brake together automatically, if the front car turns rapidly to avoid something on the road all the other cars will turn with it automatically. Of course this means getting experimental autopilot systems in production cars. It might actually be safer for the AI to drive in most situations anyways as the AI will never get drowsy or distracted, so on those long trips to grandmas you can just take a nap in the drivers seat!


DARPA Grand Challenge is developing auto-pilot for cars. They already achieved driving by GPS waypoints through the desert 100 miles. This year begins the city-driving portion including obeying traffic laws and dealing with congestion and pedestrians. With this technology and others already in production (Adaptive CC/GPS/3G wireless/WiMAX etc) personal AI driven vehicles are starting to appear quite feasible.


This has been a viable solution for years. I think people are actually over-estimating the technology requirements necessary for these systems. I think retrofitting older vehicles could even be feasible and economical. I really don't think any type of adaptive control would be required to pull this off. And forget about AI for a while, too non-deterministic for safety-critical applications. KISS.

Fairly simple sensors, nothing fancy for actuation, and not terribly computationally intensive. I think the communication is the trickiest part, but may be avoidable as a safety component.

What this tech really needs is backing to provide long-term assurance that this is the way forward. Pull some of the tech development risk away from industry, and establish some standards (rules of the road) to ensure compatibility and competition. Before you know it a new market will form (maybe trading “leader credits”?)… I wouldn’t be surprised to see the trucking industry take more interest in this.

And any mention of Microsoft comes across sounding like a scare tactic. Does anyone really think the autopilots in airplanes (or any safety-critical device) run Windows? Just from a business standpoint the cost and overhead would destroy you, and forget about reliability or certification.


when the scond vehicle finds the low pressure zone indicated it couples with the lead vehicle causing a penalty to the primary vehicle according to legend.

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