Save More Gas by Safely Following Trucks

I remember a discussion about this a long time ago, late 70's I think. The idea was a little scary: if you drove a VW Bug, and got really close behind a big rig, the draft would literally pull you along. Then you could drop into neutral and just coast the whole way. At least, that's how the story went...

Of course it's practically suicidal - you'd have to be within a dozen feet or less for it to work, with no gears engaged.

I've sometimes wondered if driving *next* to a truck, maybe next and a little behind, would have a similar effect. It would be irritating as hell to the truck driver, but at least not quite so dangerous.

I should have underscored that point. While people tried this I'm sure, and I was *wondering* about driving next to a truck, I'd NEVER do it, nor suggest anyone else do it either. Truck accidents aside (and that's not trivial), just the reduced visibility is very dangerous. Then there's the stress of trying to be just the right distance while staying super-alert the whole time... Not worth it by a long shot.

Note: I have not done any research on this specific question, but I am a physicist.

If you've ever seen a wind-tunnel test, you'll have seen the long tail formed by a car or airplane. Alongside, however, the airstream is turbulent, meaning that swirls and eddies spin off and can dramatically increase air resistance. The amount of turbulence is determined primarily by the "roughness" or irregularity of the object moving through the air (or water), and so a truck would very probably cause a lot of turbulence.

In short: I expect that driving alongside a truck would increase air resistance and thus worsen fuel economy.

mramige, did you read the section of my article with the link to MythBusters results? They certainly didn't follow a truck at a few inches. In fact they found that the gas savings was 11% at 100 feet, and I restate here, 100 feet is not a safe following distance. 

This is an interesting article. Being behind a truck would cause you to drive slower (usually) or at least keep you mostly to the slow lane, thus saving you money. And if you are very careful about the distance that you are from the truck, it could in theory provide more savings for your fuel usage.

BUT there is another risk that hasn't yet been mentioned... the fact that all trucks (especially large ones, even with mudflaps) kick up rocks at your car... that leads to dents, rust spots and sometimes cracked windshields. I've driven enough years in California on major highways to know that even in a lane next to a big rig can be a prime spot to be "hit". So that cost risk would have to be included in any "savings" you'll get from gas.

My husband and I drove from the UP in Mi to FL averaging 55 mph and trying to drive behind trucks -- although not to close and at a safe distance -- and we made the whole trip for $180! We have a Subaru that gets 28mpg in highway and the trip is about 1,600 miles -- we were very pleased and relaxed too since we weren't rushing to get anywhere! Just be safe.

I can understand driving behind a truck to combat lead-foot, and to avoid arousing the ire of other drivers, but to be safe you'd have to be pretty far back. If you're far enough back that the truck itself is not a danger to you, other drivers might start getting irritated with your speed because they can't necessarily pass you and the truck at once. Best to hang back far enough that they can pass you one at a time if you're going to try this tactic on a two lane highway or other situation where passing is difficult, but then they've got to make two maneuvers, so I'm not sure you've gained anything with regard to not pissing people off.

In the photo on this post, the perspective of the camera shows that the following vehicle is too close. If you can't see the truck's mirrors, the truck driver almost certainly can't see you--and from that close, you can't see much of anything ahead of the truck. Likewise, driving beside a truck puts you right in the driver's blind spot and blocks your own vision of the other side of the truck.

As a motorcyclist, I do everything I can to keep as much distance as possible between myself and large vehicles, and there's no way in hell I'd let one block my vision like that. Riding near a truck makes it hard to see and hard to be seen. Add in the dangers of the truck itself, like tire blow outs or insecure loads, and they've got red flags all over them. I even avoid passing them without at least one lane between me and the truck if I can avoid it, and always pass as quickly as possible so as not to be stuck next to it.

Please don't listen to this, driving behind trucks is a horrendous idea, and in fact probably the least safe spot on the freeway.
1) tires can come flying at you if the truck has a blowout
2) you will be driving in the right most lane, and people will continually be merging in front and behind you (to exit and enter the freeway)

Please don't do this, fine you want to save money and not go fast, drive in the center lane at your desired speed, it is fairly easy to pass people that don't move and don't do anything unpredictable.

A few years ago I got stuck behind a truck going through town. I quietly cursed my luck and fumed at the driver for going 3 miles in a 40-45 mph zone at 32 mph the whole way.

It was only as he accelerated out of town that it dawned on me that he'd gone 32 mph the entire way. He had driven on a busy road, at 6pm, through 8 traffic lights and never once touched his brakes! He knew what the best speed was to reach all the lights when they were green and after all the waiting cars were out of his way.

To this day it remains one of the most impressive driving accomplishments I have ever personally witnessed.

THAT is how you can save gas: no by following right behind a truck, but by following its lead. The driver's profit may depend on maximizing his mileage, so why not learn from his experience?

BINGO!  I couldn't have said it better....

Not to mention the obvious safety hazard of following a truck closely, it's worth mentioning that you'll be braking a lot more frequently than if you were coasting along at the speed limit in the faster lane, which might defeat the purpose of saving money.

In my view it's not worth it unless the highway is congested already.

I never thought about drafting behind a truck to save on gasoline. But like everyone else has commented, it is too dangerous to do.

Everytime we drive, we are taking a risk. Last thing I want to do is add to the possibility of an accident happening.

Get off your high horses.

Rush hour in any city makes it completely impossible to follow at a "safe distance". No matter how hard you try, someone will always cut you off and take away the safe distance between you and the car (or truck) in front of you.

I totally agree with Linsey and Ryan. I live in Seattle and I have to commute through about an hour of traffic and the stop and go always seems to stress me out. Over the past few months, I've learned that following (yes, a safe distance) a truck's lead not only saves gas but also lessens the overall stress level when commuting to school. Trucks to me do seem like wise big brothers because they, like Ryan previously mentioned, seem to find a happy medium when it comes to speed to avoid all of the hectic stop and go mess. Great article! I was surprised to find a great amount of negative comments.

What kind of idiot is going to follow a semi-truck at about 5 car lengths and not get antzy about it? It seems to me, at best, suicidal... let alone, illegal. Talk to a truck driver at a truck stop and see what information they have for you. How about the fact that some of the worst accidents involving trucks are the ones where cars are not following at a safe distance, or do not take into consideration the difficulties that truck drivers endure just having to share the road with these fools. I beg to disagree, the best way to save gas is not to drive.. If you must drive, do so intelligently using other fuel-saving measures, like slowing-down....
How would this person like a civil law-suit on their hands because they are recommending that prople follow at a unsafe distance? I, as well as my family, don't think this strategy is worth the price of a life. Especially if the life is someone elses and you have to live with that responsibility.
Choose your words and recommendations VERY carefully, my friend.... There WILL be people that will follow these instructions.... I just hope I never see them.

um..where do I recommend that you follow at an unsafe distance? I also said it is extremely dangerous to follow too closely and you could get pulled over.  It's funny that you felt you had to post your comment three times and show that you  never read the entire article.

It seems a lot of people are only reading what they want to read (I'll admit I read the header wrong at first too, until I thoroughly examined the article), but Xin is not advocating that you jeopardize your life by directly driving behind a semi. Sure automotive accidents may happen from trucks, but there's an even greater number of risks from driving alongside drunks, street racers, sleep-deprived/cellphone engaged people.

Take from this article and some of the comments what you will. I live around the Los Angeles area wherein people are always in a hurry and thus our glorious traffic jams. I've noticed on occasion on highways, the left-most lanes will be dramatically slow but the entry/Truck lane is constantly moving. Ironic how those lanes are supposed to be for faster moving traffic. We all want to be in constant moving traffic as opposed to stop-n-go traffic, but remember as everyone before me has mentioned, keep a safe distance while driving.

This "Apparently driving behind big trucks also saves you gas due to something called drafting, and you can safely take advantage of this to save an additional 5 to 10% of your gas." is a complete guess and completely wrong. To get any sort of efficiency you would have to be TOO CLOSE. 100 feet is not enough. You going off and GUESSING 5-10% efficiency is wrong. No, you cannot draft at a safe distance.

This is an astoundingly disappointing article. The only decent point (drive behind slower trucks to keep yourself at a slow speed) was barely touched on, then there's focus on drafting for three paragraphs. You cannot draft at a safe distance. At a safe distance you are out of any drafting efficiency.

I understand everyone's comments regarding safety concerns.

Even at a safe distance, I've been the victim of having trucks pick-up stones and loose debris on the road. Last year alone I had to repair my windshield 3 times. The year before that I had to replace the windshield.

First of all, the speed limit needs to be reduced and enforced. This in itself will save lives. It actually can be very pleasant driving at or under the speed limit. People are in such as rush just to save 5 minutes. I experimented on a little trip this weekend. I used my cruise control when possible, did not accelerate needlessly, and stayed at 60 mph. And, no, I was not the only one going 60 in the slow lane. There were others. Bottom line, even with the AC on in my 2006 Toyota Corolla, I went 163 miles on 3.67 gallons = 44.6 mpg. What do you think of that???

I drive a flatbed 18-wheeler...

The vehicles we fear most on the road, are you 4-wheelers... especially you soccer-moms in your SUV's, talking on your cell phone, and feeling invincible.

In the winter time, whenever the roads get too slippery, without fail, the kinds of vehicles we see spun off the road the most, early on, are the SUV's... we'll see probably a dozen of them, before we start seeing other vehicles get taken out as conditions get worse...

Anyways, just a mini-rant there.

You all need to understand... we're not the unsafe drivers on the road... we go through several weeks of training, before we even climb into a rig and spend several more weeks of road-training with a trainer before we're let loose by ourselves...

Any idiot can get a license for a 4-wheeler, with 75% or 80% on the test, which is usually only 20 questions.

These idiots will do just about any stupid thing you can think of on the road.

One recently, as I moved into the left lane to pass a slower truck, a white SUV (>sighs<) was racing up in the right lane to try and get through before I caught up with the slower truck, and just didn't make it and had to slam on his brakes when he ran out of space between us just as he got up to us... once I finished my pass and moved right again (only after the passed truck, signalled to me that he was cool with the space he had in front of him), the idiot in the white SUV raced past, flipping me off as he did, like I was the idiot.

If you spent time watching the trucks on the road, especially when they interact with each other, you'll start to notice that there is a lot of communication happening with each other. A lot of it is over the radio, sure. We usually know of an accident, a closed lane, a blown tire in the road, even a 4-wheeler changing a tire on the shoulder, miles in advance before we get there. (we also know of the idiot drivers coming up behind us, miles before you get to us... you know who you are.)

The radio communication is only about 1/4 of the communication happening tho.

Most of the non-verbal communication is in the light-codes we use with each other. We tell each other when they can come back in after completing their pass, thanking each other for what the other driver did earlier, if they have a problem with their securement and should pull over, if they are cutting in too close, and even if we're about to make an evasive maneuver for something we see in the road ahead, if it is a tire carcass, chair, or dead deer in the road, or emergency vehicles or broke down vehicles on the shoulder.

We know what to expect from each other, and we know, the other big-rig drivers know what to expect from us.

Even something as subtle, on a 2-lane highway, as the truck in front, moving in his lane, a foot to the right, can signal to the truck behind, that the road ahead is clear for him to make a pass, while, if we're hugging the left side of the lane, he sees an oncoming vehicle, or something else making the pass unsafe. He's basically letting you see past him, or blocking your view. We'll do the same thing for 4-wheelers behind us. Some of us will also flash our running lights on and off after the last oncoming vehicles comes by to signal the road is now clear, and make your move. Not all drivers do this signal tho.

We also, have larger stopping distances. I mention this, for the 4-wheelers that have a habit of pulling in front of a truck, with the 'safe' distance that would be ok if it was a 4-wheeler.

Big rigs, take a MINIMUM length of a football field to come to a complete stop from 55mph, on level ground, with perfect road conditions, and a heavy load which makes their brakes work most efficiently. This isn't a nice stop. This is an emergency stop. One that has a good chance of dislodging the load. Even more so if the load is coils or bundles of pipe.

Running past the truck just to jump in front of him to try and make that ramp you're about to miss, scares the hell out of truck drivers, as the 4-wheeler doing this maneuver, usually slams on their brakes as soon as they're in front of us, to make the ramp. When this happens, I'm simultaneously slamming on my brakes (which take at least a second to activate... air-brakes aren't as responsive as hydraulic brakes), and hitting my hi-beams, signalling TOO CLOSE!!!

The particular event I have in mind, I couldn't even see the back of her... yes... another SUV... I only knew she was on her brakes when the middle light at the top came on, and if she hadn't darted out of my way onto the ramp when she did, she'd be getting cut out of her SUV a while later.

If we're empty, it takes us longer to stop. Seriously.

Our brakes are most efficient with a heavy load. That's what they're designed for. When we're empty, it doesn't take much for us to lock our brakes up, and lose our stopping power, jacknife, fishtail the trailer, or even roll over.

Ok, I went off on a few tangents, I'm sorry, but I was inspired for a few minutes.

Back on topic... :)

When I find a 4-wheeler tailgating me, my response is simple.

Every few seconds, I tap on my cruise control, dropping my speed by 1mph every 10 seconds or so, until the drafter gives up and goes around.

A 4-wheeler getting on my good side? If I'm passing one, and when I'm ahead of him and ready to move in front of him, if he flashes his headlights at me (on and off, not high-beam to low-beam... high-beams mean danger, remember?), that simple act of road-frendliness tells me he's a driver that gives a damn about his driving, and respects the other vehicles on the road. Even the particular needs us big-rigs have. That 4-wheeler will earn our appreciation, and even a little bit of our respect, for driving like a professional. And, we may just acknowledge that, and say so, by giving him our flashing running-light code back at him, in thanks.

-- Smoovious
(currently at a truck stop in Salinas, CA)