Following
 

Mention the word drafting and you immediately get extreme reactions. It conjures up an image of throwing a hook over the next guys bumper but you don't have to be that dangerously close. There is still some great free air to be had behind big trucks at the rational distance of 40 meters. You don't have to be "right behind" the next vehicle. It is described right in the EcoModders hypermiling tips to drive in a "wind corridor of traffic". Following (or drafting) is not dangerous if done wisely. I have been commuting for 22 years, 80 miles a day, 80% highway. 300,000 miles of following and the worst incidents are three stone chips. I always choose to follow a big truck as my guardian.
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Yeah. It's great to sit home on the computer and fool yourself that you always drive by some arbitrary rule of thumb. Anyone that drives a divided highway during rush hour highway traffic has learned the reality of it. 30 meters following distance is accepted as normal and safe by EVERYONE out there. Drop back farther than this and someone else takes your spot. Drop back again and they cut in again. It is impossible to maintain a "two second gap". No one on the road wants it. It is a consensus. Complainers of drafting need to come in from Utopia and look at their own experience and they will see that they too follow at 30 meters regularly but just don't want to remember about it now because it doesn't fit their argument. True, some jerks weave back and forth at 30 feet and this is dangerous but 30 meters is completely normal. All day long. Every day.
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If 30 meters behind cars in traffic is ok then 40 meters behind a big truck that is mass anchored to make changes of speed and direction more slowly, on an open road, is safe. Safer than leading out on an open road by yourself wherever there are deer crossing. I feel much safer with a blocker/ guardian in front of me. They are pros and drive millions of miles per year. They sit up much higher and can see even better in bad weather. My lights work better off the back of their rig like it is day. Their actions and reactions show you advanced warnings of hazards 80 feet before you would have seen them and, you can actually see all the way up and under their front bumper anyway. Their big tires temporarily plow a clear path on the pavement from snow and standing water so I have a better surface to drive on. Hypermilers drive slower than average so now it is nice that people coming up behind you are already planning to move around the truck from much father back and don't blame you for being "some slow guy in the way". Let's change the term from drafting to following. Maybe this will alleviate some of the sour taste that seems to spit up anytime it is mentioned. Following a big truck at 40 meters is safer than driving alone and you can save 10% of the worlds remaining gas.

Paragraphs, please.

Let's count in seconds, please. Just like aero drag, stopping distances increase exponentially with speed. Freeway traffic can vary from second gear to maybe 80 mph or so. It's important to take this into account.

Given that, I'll go along with this. But remember that while you may be able to monitor traffic situations through the windows of the car in front of you, you will not be able to know if the semi is about to slam on his brakes.

I'm basing my experience on 65mph which is 1.35 seconds at 40 meters. Very comfortable. Traffic during rush hour naturally tends to gap out at 20-30 meters at the same speed. 1 second. Not just my choice. Theirs. All of theirs. A consensus.

Sendler, interesting thread. When I first listened to what you were describing about drafting in another thread, I felt that what you were doing was very dangerous. Now I'm starting to reconsider. I would never, ever do this on an open highway with light traffic because in normal driving conditions that is an unnecessary risk no matter how great the mpg gains might be. However, I very much know what kind of traffic you are describing, and if I were stuck in your commuting situation, I would probably use the same technique.
Rush hour traffic like that is always going to be dangerous and as long as you are alert (like most hypermilers), it sounds like you are one of the safer drivers on your commute.

I'll admit, this is typically what I do. Following a big truck at a respectful distance is more comfortable to me, on top of improving mileage. I also feel less desire to go faster.

Same here. I leave a minimum of 3 seconds in front of me no matter what the rest of traffic does. Tailgaters get tired and go around, sometimes they cut me off and brake check; I don't have to worry because I am ready and they are in a hurry. Ironic though, as I am traveling the speed of traffic, and the former tailgater just ends up tailgating the same car I was previously following.

Automatic drafting coming to you ...
 

Article on automatic "car platooning" by Volvo
Car Platooning successfully demonstrated for four vehicles

I think what is needed is a way to differentiate the hypermiling drafters (who are pretty safe) from tailgaters who have other motives (or unintelligently behaves like gas molecules in commuting vessels).

The new Mercedes Actros over the road truck system actually has autonomous distronic with complete emergency braking for close following. In town they use the front radar cruise with fly by wire throttle and computer controlled automatic/ manual transmission to allow automatic following in stop and go traffic to make it easier on the driver. They have even done extensive testing of wirelessly interlinking the control networks of several vehicles to form a "train" whereby the front driver controls everyone's brakes for instant response times in addition to the distronic. Complete ABS and ESP, forward night vision, lane keeping assist, blind spot assist, ect. for the tractor and trailer make for a very modern system. Imagine the billions of gallons of fuel that could be saved if tractor trailers could safely draft!
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The new Mercedes-Benz Actros | Daimler > Company > Special Topics > The new Actros

I'd hate to be the one trying to get over two lanes stuck next to electronically-connected tractor trailers. Sounds like a nightmare for the traffic around them.


But I do agree with the general premise that there are many situations where you follow closer than a usual hypermiler truck draft distance/time gap. The point about trucks not being able to slow down as quickly is one I've made before too.

Theoretical situation:

I'm following another Prius in my Prius with a 1 second gap. He slams on his brakes, full impending lockup/ABS. I have less than one second to react if I want to avoid hitting him (and can't simply swerve to another lane). This assumes he will be coming to a full stop.

If I'm following a truck that takes potentially 3-4 times as long to stop as my car, at the same distance, my reaction time to his emergency braking is longer. I don't know the math of it, but in my head it's significant. I'd probably have well over 2 seconds to react and transition to full-effort braking and not hit him, assuming he comes to a complete stop in front of me.


If anyone is having trouble visualising this in terms of braking, perhaps thinking of it in terms of acceleration is easier. Think of how much more time you'd have to react to a slower-accelerating vehicle accelerating behind you at full throttle compared to a car that could accelerate as fast as your car. From a distance at which a car with the same acceleration potential as yours would only need a 1 or 2 second jump on you to eventually catch you, a tractor trailer would need a lot longer. Of course the difference is larger between a semi and passenger car in accelerating than braking, but the theory is similar.