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July 20, 2005

Driver's Ed, Hybrid Style

Much has been made of the discrepancy between the rated fuel economy of hybrid cars and the actual results that drivers get on the road. Sure, "actual mileage may vary," but that variance proved particularly wide for hybrids, and was especially aggravating since fuel efficiency was the main reason people bought the hybrids in the first place.

Now comes the Dean of Energy Geeks, Amory Lovins, to offer a solution. According to his half-page piece in the current issue of the Rocky Mountain Institute newsletter (p. 15 of large pdf), hybrid owners need to learn a new style of driving to take advantage of their cars' technology. Lovins calls it "pulse driving," and it has two main components:
- Brisk acceleration, then letting up once you reach cruising speed. "The engine is most efficient at high speed and torque," he writes.
- Gentle braking, anticipating the need to stop. This allows the car to recover as much energy as possible and feed it into the battery. If you try to stop more suddenly, the mechanical brakes kick in, and they dissipate that precious energy as mere heat.

Lovins claims that this strategy has enabled him to eek out 63 mpg with snow tires on his 64-mpg-rated Insight, and will bring in 53 to 55 mpg on the 55-mpg-rated Prius.

Not having a Prius, I can't test-drive this advice, but I'd be curious how it squares with the observations of all you hybrid drivers out there.

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Comments

Yep, that matches my experience. I have a 2003 Honda Civic Hybrid, and my current average tank mileage is about 10% better than it was when we bought the car.

The behavior I would add to Lovins' observation is an emphasis on coasting, taking advantage of hills or upcoming stoplights to take my foot entirely off the gas.

Posted by: Jamais Cascio | Jul 20, 2005 11:17:29 AM

It's nice to find out the way I've been driving is pretty much how I'm supposed to drive. I have been getting about 45 mpg on my Civic Hybrid, which is about what it's supposed to get.

Posted by: Eric L | Jul 20, 2005 12:28:08 PM

I've been keeping it (barely) above 50 mpg in my Prius. I did make 57 following a UHaul (at a safe distance) for a few hundred miles, but that's a special case.

My experience is a pretty close match for his. I'm "modal" in the sense I'll try to keep it in electric mode using a light throttle touch, but if the engine comes on I'll accelerate briskly again.

When I first got it, it seemed to me the car responded better if you are "intentional" in your driving: Accelerate. Cruise. Coast. Brake.

Other than that, I think the easiest way for a non-expert to keep up the mpg is to get it into cruse-control as often as possible. Experts say they can beat cuise-control, but that's not me.

Posted by: odograph | Jul 20, 2005 12:59:40 PM

I've seen this advice anectdotally on the Yahoo's Prius owners group and wanted to try it. Personally I tend to accelerate in my '04 Prius very slowly, letting the electric motor get up to 25-30mph sometimes, but otherwise try to coast, use cruise control as much as possible, and do brake gradually. This has reliably given me 45-50mpg and that range seems to fluctuate mostly directly as a function of external temperature.

The Prius has also helped coax me away from any kind of tailgating I may have done in the past since tailgating brings braking, braking brings energy regeneration, and though regeneration is good, it won't match direct use of the car's kinetic energy. I've thought about affects this style of driving could have on traffic flow and congestion, but that's a separate topic.

Posted by: Patrick | Jul 21, 2005 4:06:57 PM

Friends who own hybrids have commented that having information on their current and average-over-trip fuel consumption has hugely helped them adapt their driving styles.

My vote: require those electronics in all new vehicles. It would cost very little and make all drivers aware of their wasteful driving styles.

Posted by: Maarten | Jul 22, 2005 9:50:43 AM

Sure enough -- and it also works for older vehicles.
I love my 1990 Volvo 745 Turbo Wagon, except for 17-18 mpg.
As a retired Aerospace Engineer and Solar Society member since the 60's, I added PV panels to our home in 2001, and have acutely watched fuel cells since Ballard started with buses. Hybrid development has gone well, thanks to genuine pushes from Honda and Toyota - very tempting.
Sooo, I dropped my highway cruise control to 62 mph from 75, lightened my resistant lead foot, enjoyed the scenery rather than blasting down the freeway with all those top-heavy SUVs, and found my gas milage came up to 23-24 mpg. Not stupendous, but still satisfying -- until used Prius prices get down!

Posted by: Wilkie Talbert | Jul 23, 2005 4:07:10 PM

Although I agree with Amory's comments on braking I do the opposite on accelerating. I try to let the electric motor run the car as much as possible and thus accelerate gradually so as not to force the gas engine on. The last tank I measured on the Prius was 53.4 mpg and that is after just 7 months of driving. I would like to hear more comments on this.

Posted by: Baiss Eric Magnuson | Jul 28, 2005 8:30:17 PM

As one of the drivers in the recently completed 110 mpg, 1387 Prius mpg marathon on a single tank of gas, I'd like to add my thoughts.

I haven't read Amory Lovin's advice yet, but have been reciting text from his book 'natural capitalism' for many years now, and know he's a very smart man. But there are differences between the various hybrids.

In a Prius, whenever you let off the gas the gas engine stops running and the electric motors act as generators, capturing energy to be stored in the battery. This also creates some drag, so if you gently depress the accelerator you gan disengage those motors and freewheel long distances as you 'glide', the term we use for this form of coasting and the primary technique responsible for our record tank.

We pulsed and glided for the most part between 30-40 mph. Any faster than 41 and the engine is forced to spin to protect the motors, creating more resistance. While it may not be practical for many people to constantly vary their speed that much, if you glide at every opportunity you'll see dramatic improvement. I routinely get 60-70 mpg in my prius on a commute that includes 15 miles of country road and 15 more of interstate, where I just set the cruise on 55 mph.

Another key strategy is to anticipate terrain and traffic patterns and use them to your advantage, slowing down before cresting hills knowing that gravity will get you that speed back 'free' in no time, minimizing your need to use the brakes. I suggest the following order of preference for techniques to slow down: glide, coast, light brake, firm brake. The more you practice the more you'll be able to avoid ever engaging the brake pads unless you need to come to a complete stop.

Finally, inflate your tires to the maximum sidewall pressure, not the car maker's reccomended pressures. This decreases the rolling resistance without any detrimental effect other than a little firmer ride.

Hope that helps,

Dave Bassage

Posted by: Dave Bassage | Aug 10, 2005 8:55:25 PM

Hi everybody,

We have had an '04 Prius for 10,000 miles. We reliably get 52 mpg on the highway and mid-40's mpg in the City (Washington, D. C.) This city mileage is far below the EPA rating, which says we should be getting 61 mpg in city driving. Neither we, nor our neighbors who've had a Prius longer than us, believe that city rating reflects actual conditions. The highway rating is about right but the city rating is way too high for normal driving around us. To Toyota's credit, we were immediately told when we first asked about the Prius in the showroom that we would not get the EPA mileage.

We are going to try to apply pulse and glide driving techniques but we're not confident there's many real world situations where that method can be consistently used.

That said, the Prius is a great car. We would strongly recommnend buying one.

Best regards.

Posted by: John | Sep 13, 2005 5:09:46 AM

I get 57mpg with my Prius using the techniques talked about. I also try to plan my routes where there are long stretches of road with downhill grades. The downhill grades are what really help maximize the cars efficiency.

Posted by: chris | Oct 14, 2005 10:58:34 PM

I get 57mpg with my Prius using the techniques talked about. I also try to plan my routes where there are long stretches of road with downhill grades. The downhill grades are what really help maximize the cars efficiency.

Posted by: chris | Oct 14, 2005 10:59:01 PM

I love my 2002 Prius. An I plan to try the "pulse" driving. However, I find that the A/C is the MPG killer. This makes sense from my physics background. Anything that dissipates energy is the enemy. Ever wonder why highway mileage is always better, even though aerodynamic drag is worse? That's because it is the brakes that really dissipate the car's kinetic energy. If you drive any car without stopping, you'll get much better mileage. Actually, "jack rabbit" starts use the gas engine in its most efficient mode. The problem is the stopping at the next light. I get 53.5mpg in my Prius on my regular route by "timing" so I hit mostly green lights, and do not have to brake much. This will work for any car; my 1979 Mercedes 240D gets 33mpg this way. Keep moving and save that kinetic energy!

Posted by: Till | Nov 13, 2005 6:18:17 AM

Another 2002 Prius driver, with experience not much different from the mode. Maarten's point, as I read previously from Bill McKibben, is well taken: most vehicles would get better mileage from the same strategies, and if all cars were required to give moment-to-moment feedback on mileage, I think many people would find themselves compelled to maximize it. I was always an inveterate speeder, for years; I tried to maximize distance covered, partly to alleviate boredom on long trips by playing the only numbers available to me. In those days I got restless if I couldn't hear the engine straining; now I cringe at the same sound, having come to associate it with a catastrophic drop in the green bar of mileage. I'm equally obsessive, I'm just optimzing toward a different goal now. Indirectly, it changes everything.

All that said, I get about 40mpg over time. It might be more if I drove more--I obsess, where my wife (who drives around down on a daily basis) pays less attention. The long-term average tends to creep up a smidge when I drive it over a distance. I generally get better mileage than the cruise control gets for me, but I can't quite say how; I guess I've been leaving it to some non-verbal part of my brain. I am intrigued by the notion that quick starts are relatively efficient; I've been assuming otherwise but indecisively so. Also have not heard of gliding and will see if I can find the correct pressure to try gliding where I have hitherto been coasting. Do I understand correctly that it doesn't work above 40mph though?

The most dramatic determinant of mileage I can discern is slope, and I spend most of my time trying to work around it. This too is something of an aggravation for drivers around me, and I wonder sometimes if it's responsible for the "gutless on the hills" concern about hybrids that I've often heard; and that leads me to suspect, as someone indicated, that more Prii on the road would change the overall flow of traffic.

What I most want: an LED display on my back bumper that displays my speed and MPG in real time, just as I see it on the dash. That might explain what I'm up to, for some of those agitated tailgaters...

Posted by: Robin Tell | Dec 12, 2005 11:55:53 AM