Auto Drafting Mode to Save Energy

[Snowstorm]

I used to remember closely following tractor trailer trucks to maximize fuel economy back in the ICE days, and a though occurred to me that with the right software tweaks, our Tesla Model S/X autopilot be can really good at this.

It was reported that by closely following a truck, one can save 10% energy at 100ft, maybe 40% energy at 10ft when moving at say 90km/h (55mph). Hey, Mythbusted did it, so it must be true right?

Want to Save Gas? Follow That Truck!
MythBusters (2007 season) - Wikipedia

Now, 100 ft is really too close for comfort at highway speeds and 10ft is blatantly unsafe. However, given that a Mode S/X can brake harder than a truck and autopilot reaction time can be a lot better than human, there may exist an auto-draft mode that would follow a large truck at say 50ft and allow the following vehicle to save 20-25% energy, pretty significant. 50ft is about 0.5s at 60mph/100km/h, probably well within reason for autopilot reaction time.

Imagine, instead of 200wh/km we would do 150wh/km going at the same speed.

 

[brkaus]

No stopping performance will help if the truck slams into something or drives off the road.

 

[BluestarE3]

Of course, you'll need to get bio-weapon defense to filter out the diesel fumes you'll be sucking in.

 

[Snowstorm]

No stopping performance will help if the truck slams into something or drives off the road.

Seems like a smallish risk, trucks don't slam into thing much more than any other car, including the one we would be driving. Perhaps there is a way to see around or under the truck to see what's up ahead to give you a split second more reaction time, but that is just gravy.

 

[chillaban]

Smallish risk, almost sure death due to a mismatched collision is the consequence.... but hey I get to go another 50 miles, totally worth it!

 

[eye.surgeon]

It's illegal, dangerous, causes road rage, greatly increases your risk of an accident, is highly likely to rock chip your front end and/or windshield, and saves you less in electricity than you likely have in couch cushion change.

Other than that it's a great idea.

 

[chillaban]

I mean, in all seriousness, I do believe that V2V convoying will be a great way to save gas once we master L5 highway autonomy. But right now all ADAS systems on the market requires the human to be able to supervise the car's operation and take over at any time. That's simply incompatible with drafting beyond human reaction time.

In theory once we have mature V2V technology, several vehicles can convoy together and serve as each other's eyes. When the frontmost vehicle sees a problem the pack can all brake and scatter.

But I see no way to "safely" draft trucks with any of the technology we have. Accidents are all about low probability events, and the risks involved with drafting a large vehicle that obstructs your views are quite non negligible.

 

[Joe F]

Ever see a tractor blow a retread? Do you really think it's wise to be 50 feet behind it? Or even 100 ft?

Ever see a tractor run over road debris and fling it in your face at high speed?

Wishing you the best of luck in your future drafting cost savings experiment. For me, that cost is too high.

 

[St Charles]

It's illegal, dangerous, causes road rage, greatly increases your risk of an accident, is highly likely to rock chip your front end and/or windshield, and saves you less in electricity than you likely have in couch cushion change.

Other than that it's a great idea.

All of this in spades, but rock chips are almost a 100% certainty in very short order. The added range isn't worth the paint/windshield damage. Also, large trucks tend to just run over road debris like tire chunks. To me, no amount of extra mileage is worth a fender/bumper/hood replacement.

 

[TexLaw]

I always love the idea of drafting, as well. Under controlled conditions, it provides great advantages. Unfortunately, the current highways are something more like the wild west rather than a wind tunnel in a lab.

Yes, it could be nice when we get to a point. Really, TACC as it stands already is "auto-drafting," but it does nothing with regard to other risk avoidance or mitigation. Until AP is much, much better at avoiding problems, you're much better off driving the car manually (or, at least, with both hands firmly on the wheel, both eyes well on the road, and your foot covering the brake pedal).

Right now, any attempt at "auto-drafting" is trading away dollars worth of risk to gain pennies worth of energy. I expect to pay all of about $700 or less to charge my MS over the next couple of years (the term of my electricity contract). Shaving 10% or even 20% off that at the risk of following big rigs too closely just doesn't make sense at this point.

Bottom line: Yes, it sure would be nice somewhere down the road. Right now, though, there are more important issues to conquer.

 

[Reciprocity]

You do not have to draft off a semi to see improvements in range, any vehicle will help break up the air directly in front of the vehicle. Certainly not worth the risk to draft off a large semi due to the potential for death if something does go wrong, but drafting off a large van or pickup at a safe distance, 2 additional car lengths for every 10 MPH above say 45? At 65 and 6 car lengths for example, you can easily attain 250Wh/mile in the Model X.

 

[OBX John]

I see close drafting convoys in our FSD future, but the other posters make good points about trying to save pennies while risking a $1500 windshield behind a truck.

 

[Derek Kessler]

I've done it once — not to save pennies, but because I was driving into and out of the West Virginia wilderness and needed to conserve enough range to get back to the Supercharger.

 

[artsci]

Drafting is only advisable when your think you'll be short of range to reach the next supercharger or other charging source. I've done that a few times and it's saved me in those situatiions. And as @Reciprocty notes, you don't need to draft a semi. A large van or SUV serves the purpose quite well.

 

[AmpedRealtor]

And what do you do if Autopilot doesn't react, then what? What do you suppose Tesla's legal liability would be for designing a mode that flies in the face of basic safety rules and recommendations put out by almost every state in the union? If this is a risk you are willing to take, and risk the lives of others in order to get a few extra miles out of your battery, that's on you. But suggesting that Tesla design a mode that puts drivers into a potentially dangerous situation is going too far, IMHO.

 

[Reciprocity]

And what do you do if Autopilot doesn't react, then what?

Autopilot doesn't drive any differently then I would in that situation, just more consistent. I pay more attention to whats going on and remain more ready to slam on the brakes with AP engaged. The only difference is that i would normally pass everyone I see in front of me and now I spend more time trying to find someone to follow. I think my driving now is way more conservative and safe then it was before EV/Autopilot. I find that AP allows me to scan farther ahead and be more ready for issues and not trying to pass every car is making me a safer driver and able to focus more on what is directly in front of me instead of checking my blind spot to pass every car.

Whats odd is that I could probably save gas in an ICE by using the same method, but I dont. Its not really range anxiety as much as it is trying to win the game of being as efficient as I can possibly be. I think the energy graph does as much to change the way I drive as the range.

Certainly, everyone should drive safely and if you are going to trail someone closely, you need to pay extra attention to whats going on further down the road and not just what is directly in front of you.

 

[JHuberman]

It improves the mileage of the vehicle you are drafting.

 

[Austral]

Drafting is actually tailgating and it's one of the top three most dangerous moves a driver can make. Different vehicles have different braking distances. Sometimes the same make and model will have different braking distances based on OEM part life cycle, after-market part life cycle, vehicle weight-related mods, etc. If you are a tailgater and you haven't crashed you, you will. The only question is who will you hurt or kill. It's too easy to get a license in the US. This discussion would not exist in Europe.

 

[Snowstorm]

I am not saying drafting or closely following is safe as it exist today. There are many variables involved but human reaction time is the most significant factor as the actual braking distance apply to both the car you are drafting and you, making it a relatively non factor. What I am suggesting is that as driver assistant technologies improve, there would be a day (maybe we are closer to it than we think) that close following can be done safely. When that happens, vehicles should have a mode that allows them to closely follow, improving the energy efficiency of all cars involved.

We bulk at the concept specifically because it is deemed as unsafe. But what if near instant reaction time and near flawless detection capabilities makes that possible? Train cars follow each other very closely, and we are OK with that because we believe the mechanical linkage allows near instant reaction time and detection (obviously), so if cars can do that too due to improved automation capability, then why not?

 

[kort677]

Drafting is only advisable when your think you'll be short of range to reach the next supercharger or other charging source. I've done that a few times and it's saved me in those situatiions. And as @Reciprocty notes, you don't need to draft a semi. A large van or SUV serves the purpose quite well.

Agreed, any larger vehicle will do, as for drafting programs, we all ready have one! AP set at 1 or 2 provides plenty of spacing. Pay attention and you should be ok