Hypermiling Makes for Unsafe Driving

OK, so remember when we told you about hypermiling in our Gas-Saving Moment of the Day? In that post, we warned of hypermiling's less-than-stellar record when it comes to safety. Well, now AAA has weighed in as well.

The association released a strong warning against gas-saving practices that can endanger lives due to poor — and sometimes illegal — driving techniques. They're talking about practices such as drafting off other vehicles on the highway by tailgating, as well as rolling stops and turning off the ignition entirely while driving. (Do people actually do this? If so, let us know in the comments.)

Other practices straddle the line of acceptability. For instance, drivers with manual transmissions often coast in neutral to save fuel. The practice is not uncommon, but safety advocates worry about drivers not having full control of their vehicles. More controversial is using neutral with an automatic transmission, although some hypermilers claim they can use this practice safely. AAA also doesn’t mention that there are various local laws against improper driving, like not having a car in gear.

Let us know what you think of hypermiling's more extreme gas-saving practices. Do you use any of these techniques? Should specific laws be enacted to restrict dangerous gas-saving practices?

AAA Cautions Against Hypermiling (TechnoRide)

Comments

Why use neutral, especially on an automatic? When you leave the car in gear and you're not pressing the gas, the engine is being propelled by the car's momentum rather than fuel--right? Putting the car in neutral causes it to burn fuel in order to keep the engine idling.

When stopping with a manual gearbox, I leave it in whatever gear I'm in until the engine RPMs drop to close to idle, then put it into neutral. I don't downshift 6-5-4-3-2-1 when stopping, as it's not as smooth.

Segfault,

"When you leave the car in gear and you're not pressing the gas, the engine is being propelled by the car's momentum rather than fuel--right? Putting the car in neutral causes it to burn fuel in order to keep the engine idling"

You're joking right?

taking your foot off the gas doesn't stop the engine from idling in the loosest sense. It's always idling unless you're in a hybrid or other stop start cars.

There's a 6-mile stretch of interstate on my morning commute that's a steady decline down a mountain. I've often shifted to neutral when there's nobody else out there because I figure 500rpms @ 70mph has to be more fuel efficient than 2900. I was bad after the last hypermiling article and tried turning off all the accessories & cut the engine turning it to ACC so I'd wouldn't risk steering wheel lockout. I know with the 03-07 Corolla the braking system has enough power for one emergency braking while the engine is not running. I didn't have power steering, but who needs it @ 70mph. I picked up about 45 miles on a tank of gas, or about $5 for the week. Don't think it's ultimately a good practice because there are those of us that would really get into bragging about how many mpg's we've picked up....GUILTY.

When turning the engine off while coasting, don't leave it in ACC. While in neutral, turn the key to ACC to cut the engine, then turn it back to ON to make sure everything still works (like your turn signals).

There are plenty of situations where it may not be safe to do. But if you are familiar with the road, there is little traffic, few sidestreets or driveways for people to come out of in front of you, and you fully understand how your vehicle handles under no power, then I don't see how it could be unsafe.

Of course AAA is speaking out against it. They don't want the average driver to start doing this improperly and cause collisions.

I've started turning the engine off at intersections where I am well aware of the signal timings. Some lights are red for almost 2 minutes! I'm sure they're longer is other areas, but even 2 minutes is a long time.

I noticed last week a Volvo in front of me did the same exact thing!

Can you all tell me where you live - so I can stay away from all of you? You're gonna kill someone, and I don't want it to be me. What is the mpg of a funeral procession???

Spanky-

Turning off a car while it's in motion (especially down a mountain) sounds crazy and dangerous to me, especially someone who is a poor, inexperience driver (not saying you are). I'm sure you were as safe as you felt you could be, but still, I would never turn off my vehicle while in motion.

Also, from my understanding, it is much safer to shift into a lower gear when going down a mountain, rather than use your vehicles brakes or put the vehicle in neutral. It may put more wear on the transmission, however, you will not overheat your brakes and then may not be able to stop halfway down the mountain.

Without any of those stuffs mentioned above, my last tank got 38.9 in 100% city driving. Why do I even bother?

Liger:

Read my comment:
"that's a steady decline"

Also you're missing the point. I did this as an experiment for one week. You're not doing it to save brakes, you're doing it to save gas. I never had to touch the brakes because it is a "steady decline."

Also you said "especially someone who is a poor (driver)" What does that have to do with anything?

The point of the discussion is hyper-miling and safety. Yes, if you know what you are doing (famous last words) you can save gas with certain techniques...is the risk factor worth it? I have already weighed in on that one...thank you.

1. an automatic trans creates a little bit of friction when coasting in gear. it does make a difference when you are going on a long downhill -- "Neutral" allows you to coast farther/ faster. but then, you're also speeding up from a (hopefully) legal and safe speed up to an illegal and usafe speed. unfortunately i've done this several times (but on empty country roads ... ).

2. i turn off my engine on this big hill when going home, because it's always packed with literally like half a mile of stop-and-crawl traffic. so since i'm mostly stopped or going less than 5-10mph, no power brakes plus working e-brake works. and i'm (mostly) not one of those idiots who weaves left and right in such traffic conditions, so power steering has no real value.

the worst was when i forgot to get gas in the rental Mustang in Maui. i had about a gallon left when i was on top of the mountain. so i coasted down most of the mountain, twisty roads and hairpins and all, in neutral and engine off. it was i think a 15-mile long mountain road. not proud of it, but no close calls.

3. DonB, i live in Mass and routinely travel I-95 and highway 24, so watch out. although i don't hog the left lane until the last moment, just to cut across 4 lanes of traffic to exit, like LM commented on the way too many people drive here. so, again, watch out for drivers here. i actually am looking to move out. hahaha

I'm not sure how much fuel this would actually save, but on my gear-shift there's a 1,2,3,D selection for the forward gears

So I use those to simulate a manual tranny

....for example, coming off a red, im on 1, release the gas and go to 2...and so on

which reminds me (im doing all caps to get one of the experts on here to give me an intelligent answer)
DOES DOING THAT SCREW UP THE TRANSMISSION????

Everyday i go to college there is a traffic light before the entrance. I turn off my engine and coast for two miles, disregarding 12 car behind me, and turn the engine on if the light is green and not in motion. If the light is green, i use the stick-shift to turn on the engine instead of the starter, it is more efficient. Doing this behavior i save about 1/2 a gallon per week with my suv. $2 saved! I been doing this behavior even when gas prices were at $2.

If you put your car in neutral while coasting, your vehicle will use gas to maintain idle. If you leave your car in gear, the engine may be turning 2,500 (or whatever) RPMs but the fuel injectors are not feeding fuel to the engine, it's basically a big air pump when in gear and coasting. This tidbit has been discussed in Click and Clack Talk Cars and Ask A Mechanic on another site. So, a car is more fuel efficient when left in gear while coasting than being put in neutral. That is, unless you turn the engine off, which is purely idiotic.

Hypermiling may be fun as you attempt to get the highest yield per gallon of gas, but it's a traffic impediment and should only be practiced when there are no other cars on the road.

Fred:

"the engine may be turning 2,500 (or whatever) RPMs but the fuel injectors are not feeding fuel to the engine, it's basically a big air pump when in gear and coasting"

Pray tell...in an internal combustion engine...if the fuel injectors are not feeding the engine fuel....how is it still running? Your car is always squirting gas through the injectors you dope. Sometimes more than others. If there were no gas, there would be nothing for the spark to ignite.

Spanky, Fred is not a dope. All modern engines have electrically operated fuel injectors. The ECU does not open them (and thereby cause them to supply fuel) when the vehicle is on the overrun (i.e. when it is in gear and the vehicle is pushing the engine). This applies to both manual and automatic transmissions.

Coasting down a gradient with the transmission in neutral will cause the ECU to provide enough fuel to keep the engine idling. Doing the same with the engine in a gear will cuase the ECU to shut off the fuel.

Choosing a suitable gear, so that you need to use niether the brakes nor the accelerator to maintain your speed, will therefore use less fuel than putting it in neutral and coasting.

Even though the engine is receiving no fuel under these conditions, the alternator still produces power, the power steering still works, the A/C still works, and the brakes still have a vacuum to provide power assistance.

Graham, thank you so much for elaborating on my statement. Perhaps Spanky needs to update his information on the engines of today.

It's true Spanky ... when an engine is coasting in gear, there is no fuel being delivered to the cylinders and there is nothing to ignite. As I said, the engine just acts as a big air pump. Air in, no ignition (no fuel), air out.

My appologies to Fred. I thought the only engines that did that were the "cut off at stop light" variety (similar to golf carts). After more research, you guys are correct. So I tried coasting in gear this morning on my 6 mile section of down the mountain interstate. I made it almost 1/2 mile before I needed to hit the gas again and had to set the cruise to maintain 70mph. In my case I'd still save more $$ by switching to neutral because even though I'm using more gas than I would be in gear at any moment in time, i'm also not applying any extra gas (or brakes) for 6 miles. It would have to be a really steep hill (or short) for coasting in gear to pay off. Joey Tribiani says the point is moo.

I've done the "Engine off" thing in the past with various cars I've owned. Sometimes just to test (on a private, empty road) just how the car would react if the engine died or failed.

Well I tried it with my 'new' Toyota and the "powers that know better than me in Tokyo" programed a fault-trip in the power steering box. Basicly if you try to drive with the engine off, the warning light comes on for the power steering and it's off to the dealer for a $200 reset.

Remember when Toyota finally does rule the world, you won't need to drive they'll just send someone from the service department out to get you.