How do truckers feel about drafting?

From my one cross country drive many years ago, I think truckers are fine with drafting (but don't get rediculous by, say, drafting at 60mph at only two car lengths behind the truck).

In fact, I usually found truckers to be the most cooperative and courteous drivers out there, e.g., if I was driving at night and trying to pass a truck, the trucker would almost always flash his lights to let me know that I could safely return to his lane in front of him.

 

If you are close enough to a semi to draft, you are an idiot. You better hope the trucker doesn't need to stop quickly for something you will not be able to see. If you are far enough back to be safe, you aren't drafting, you are hanging in the swirling air behind the truck.

 

If you draft then make sure you don't draft in between two trucks or your Prius may end up looking like this...

 

Close Drafting semis is one of the worst things from a PR standpoint you can do in a hybrid. Truckers join CleanMPG, An authoritative source on fuel economy and hypermiling to rant about alleged legions of hypermilers that virtually hitch themselves behind the 18-wheelers. Such drafting works, but the only way you are going to make an exit is if you know the route in your sleep or have a nav device...at any rate this is very bad publicity that makes it harder for people to turn in their gas guzzlers or hybrids and Prius. Trucking forums have discussed it, sadly with a lot of misinformation.

<IMG style="MAX-WIDTH: 800px; ; WIDTH: expression(this.width > 800 ? 800: true)" alt="" src="http://www.cleanmpg.com/photos/data/519/blindspot_overhead_1_.gif" border=0>

This illustrates the "No Zone" - I stay out of those areas.

 

Safe Drafting Distance?

Does anyone know if a truck is going 60 mph, at how many car lengths behind the truck will there no longer be a drafting effect?

 

Re: Safe Drafting Distance?

I've answered my own question. According to Mythbusters' tests, here's the percentage improvement in gas milege at different feet behind a big tractor trailer going 55 mph:

10 ft. = 40% improvement

20 ft. = 27% improvement

50 ft. = 30% improvement

100 ft. = 11% improvement

When I took drivers education 35 years ago, I was told that a safe trailing distance between cars was one car length per 10 mph. This means that at 55 mph, a safe distance would be around 92 feet (assuming a car length of around 200 inches or 16.67 feet).

According to this rule of thumb and Mythbusters' tests, one can travel at 55 - 60 mph at a safe distance of 100 feet behind a big truck, and still get a decent amount of drafting effect -- around an 11% improvement in mpg.

 

Does anyone know where the area of disturbed air is behind an 18-wheeler? It is an uncomfortable place to be, and I have assumed it is not beneficial to mpg. Is this area within or behind the 90' to 100' zone noted by Boo?

 

Re: Safe Drafting Distance?

 

I follow truckers back far enough that other vehicles can cut in because truckers are my 'pace car.' Seeing a truck ahead, the faster traffic will smoothly pass me and the truck without tailgating or otherwise being a pest. This lets me cruise at 65 mph where my MPG is excellent.

Bob Wilson

 

I think a lot of truckers like drafting, they do it with other trucks all the time. I drive on I-5 and it really gripes me when four or five trucks are traveling less than two car-lengths apart in the right lane. Entering the freeway means coming to a halt to let them pass or trying to slip into one of the tiny slots between them. Oregon allows triple-trailers (one truck pulling three trailers) and if I see one I always give it a WIDE berth. That third trailer dances all over the road.

 

Re: Safe Drafting Distance?

 

Yes, that was my experience many years ago on my cross country trip. I would frequently run into 2, 3, 4 or 5 truck convoys drafting each other. If I drafted behind the convoy at 100 feet at 60 mph, that was always a lot longer than the distances between the trucks.

 

Boo and others who think tail-gating a truck is the road to economy I refer you to the 2 second rule.
Hazard Perception - The &ldquo;2 second rule&rdquo; - Transport SA

Also to save time later look up the phone number for your local touch up guy who can fix the extra stone chips you get from following too close. Write the number on your hand book.

In South Australia 33% of accidents are from following too close. I suspect the USA has similar statistics.
Have a look at this
Hazard Perception - The &ldquo;2 second versus 1 second comparsion - Transport SA

 

Just in case anyone missed it or just skimmed over it, please read this again:

It's a good technique. Makes everyone happy, is perfectly safe, and is good for mpg.
I have been doing the same thing for about 15 years both in the US and here in Germany and occasionally other EU countries. The best following distance varies according to traffic density and proximity to large cities. In heavy traffic in a large city, you have to follow much closer than in light traffic out in the middle of nowhere.

Regarding the original post, how do you feel about people drafting behind you?

 

Hi All,

To get an advatage from drafting, one needs to be closer than than where the sheer vortices start forming off the back of the truck. If you feel the front of the car buffeting, your too far back and the mileage will be worse than in clean air.

But this is damn close in typical metro-area driving, where trucks rarely do over 65 mph. Its just not a a safe or practical thing thing. Especially with the way the yahoos cutoff other vehicles doing a few mph slower than they want to go. Besides with all the other vehicle wind disturbances, the air is just not calm enough for a good vacumm to be setup constantly. I actually try for the reverse, and get into areas where the car is in the cleanest air during the highway portion of my commutes.

Out on the interstate at 75, in cold dense air (15 degrees or so), its a whole other thing. One can be quite far back, and still get sucked along. It can actually be difficult to avoid being pulled in too close. Have a truck pass you at this speed and temp, and you may actually need to apply the brakes to prevent the additional draft from pulling you too close to the truck in front.

 

Yes, some of us Truckers do draft each other, but we often ask on the CB if the other trucker doesn't mind. We'll often swap places if the ride is long enough so each of us can get some benefit from a "draft".
But please don't draft me in your car, I'm normally driving a 35 foot box truck, and I can't see you behind me! (If you can't see my mirrors, I can't see you!) Besides you'd have to be on my Tommy Lift to get any benefit by drafting me. There's a lot of open space under the box of my truck and it stirs up quite a wind at speed. (55-65 mph)
A secondary thought is that most trucks kick up a lot of road debris, pebbles and what not. If you're on my nice person most of this stuff is going to hit your car and cause paint damage or maybe even damage your windshield. Is it worth it???

 

Hang around on some of the truckerforums, like roundtable.truck.net
and thetruckersreport.com, and look for discussions of 4-wheelers.
.
Basically they hate drafters, and think nothing of drifting
the trailer over toward the shoulder to kick up all the crap
laying there to spray all over a following car. The Smith
System of safety training, and discussions I've had with a couple
of drivers, say that FOUR SECONDS is really where anyone should
be [and that includes trucks following other trucks, those "conga
line" scenarios you often see are NOT safe or condoned].
.
You also don't want to be back there when a truck sheds an
"alligator", i.e. retread, or runs over something that won't
harm it but may very well clobber your underside pretty hard
before you have a chance to evade it.
.
Bottom line -- stay the hell out of there.
.
_H*

 

Thanks Pat.

Actually, I care much more about safety than fuel economy or anything else when driving -- I'm a stereotypical Volvo owner and I hardly ever try to maximize gas mileage on my Prius. When I did my cross country trip about 34 years ago and drafted whenever possible, I was going for fuel economy because I was poor, and I thought I was doing it safely without tailgating. Since then, I've never intentionally drafted behind anyone.

I'm more shocked at the fact that I was taught the 1 car length per 10 mph rule (which is basically the 1 second rule), and never subsequently heard of any other rule, let alone the 2 second rule or the 3 second rule which are 2 or 3 times the safe trailing distance I was taught.

Live and learn. Maybe governments should institute continuing driver education or re-licensing requirements. It would be a good thing if drivers were required periodically to re-learn what they were initially taught and to learn what changes have occurred in the law and perceived safe driving practices (even if such safe practices are nearly impossible to observe in moderately dense traffic).

 

Someone else mentioned a salient point: "How do you feel about being drafted?" You would call it "tailgating" and get mad at the other driver. For the safety risk and the amount of anger you can instigate on the road, I think it's not worth a tiny bump in MPG.

Here's an illustration with some of Boo's numbers:

1. I'm traveling 100 ft back from a car at 60 MPH.
2. My car's hard stopping distance at that speed is 143 ft. Theirs is less.
3. They panic-stop.
4. I react with inhuman-lightning-instant-reflex, let's say 0.5 seconds before applying full brake, meanwhile the gap is reduced by 44 feet, leaving a very small margin which is partly, if not completely consumed by the difference in our stopping distances.
5. Best case outcome is that I stop within inches their bumper.

In reality, a lot of factors reduce reaction time, and our own confidence in our driving abilities makes us forget that not everyone else is a competent driver, and that the unexpected is called unexpected for a reason.

I challenge everyone reading here to try driving the same speed, but with a 4 second following distance for a week. I think you'll find what I've found:

1. Driving is a much more relaxing experience.
2. All those people you thought were "cutting you off" by filling the gap, only move on to another gap and hardly impact your moment-to-moment driving, and have no impact on your time-to-destination.
3. You feel much safer and begin to wonder if everyone else on the road is completely insane.
4. You still end up passing the cars who raced by you a while back... this always makes me laugh. Someone speeds by, weaving in and out. They aggressively tailgate in heavy high speed traffic, and when they've gained a few car lengths on you, their exit comes up. They barrel across 3 lanes to make their exit, and then as they're slowing down, you zip by. This happens to me every time I'm on the freeway, and it makes me want to follow these people and hand out medals because they "won."
5. You promote better traffic patterns. When someone ahead brakes for some unknown reason, you have LOTS of time to decide whether you really need to slow down. 9 times out of 10 you don't brake, and a little "wave" in traffic is removed, saving you and everyone behind you some gas from unnecessary slowing/accelerating.
6. You still get where you're going... somehow miraculously in the same amount of time.