Archive for July, 2011


July 6th, 2011 Comments off

Apparently, all of my blog posts since February of this year have involved me complaining about someone else for getting it wrong.  From the media’s promulgation of inaccurate information, to Saab’s inability to correctly mount tires, it seems all I’ve done recently is look for ways to point fingers and criticize.  And that’s just not healthy.  In the midst of it, ThatCarBlog‘s second anniversary came and went (my Inaugural post was June 26, 2009) without so much as a self-congratulatory pat-on-the-back.

So as I begin my third year of randomly typing words about cars whenever I get a few spare moments, I’m going to be more positive.  And that means looking for opportunities to point out when other folks get it right.

Roland Hwang got it right.  In his June 29 post on the National Resources Defense Council Staff Blog, Mr. Hwang describes the auto industry push-back as a result of the Obama administration’s suggestion that the CAFE regulations for light-duty passenger cars and trucks in 2025 should be 56.2 mpg (which is eerily similar to the push-back at every past attempt by the feds to regulate the auto industry, whether it be seat-belts, air-bags, catalytic converters, or the removal of lead from our gasoline).  There’s really nothing I can add here – Roland beat me to it.  Click the link and read it for yourself!  (The irony isn’t lost on me that, in my attempt to commend another for a job-well-done, it is to some degree Mr. Hwang’s criticism of the auto-industry that I am commending…)

But why do we use miles-per-gallon (mpg) as the metric to measure fuel efficiency?  It’s the amount of fuel we use that is of primary concern – not how many miles we drive. Since the dependent variable (gallons) is in the denominator of the mpg metric, we get a skewed sense of actual fuel efficiency.  As cars get more fuel efficient, people overestimate the benefit of additional mpg improvements. [Richard Larrick and Jack Soll, of Duke University’s Fuqua School of Business, wrote about this “MPG Illusion” a couple of years ago, and it’s worth a read.  For example, most people tend to think that improving a vehicle from 34 mpg to 50 mpg (a 16 mpg improvement) would result in greater fuel savings than an improvement from 18 mpg to 28 mpg (a difference of 10 mpg).  In actuality, it is the latter case that provides more benefit – more than double the fuel savings of the 16 mpg improvement in the already-efficient 34 mpg vehicle.]

The reason for this can be seen in the graph below.  The big-red-line illustrates how mpg (on the x-axis) relates to fuel-consumption (in gallons per 100 miles, on the y-axis).  On the left (steep) side of the curve, small mpg gains result in large reductions in fuel consumption.  However, as cars become more efficient (and we move to the right side of the curve), it takes quite a large mpg improvement to result in any significant fuel reduction benefits.


So, what does this mean in the context of CAFE regulations?  When NHTSA implemented the first regulations (of 18 mpg) for model year 1978, it meant passenger cars would use about 5.5 gallons of gasoline to go 100 miles.  Seven years later, the CAFE regs were 27.5 mpg – a nearly 10 mpg improvement, resulting in a fuel consumption benefit of nearly 2 gallons per 100 miles.  The regulations stagnated here (and actually went down slightly) until 2011, when they started rising further, to 39 mpg for 2016.  This 14.2 mpg improvement over the 1985 regulation saves just under 1.5 gallons of gasoline per 100 miles.  (Notice that?  The 14.2 mpg improvement between 1985 and 2016 actually saved less fuel than the 10 mpg improvement between 1978 and 1985.)

For 2025, the administration is proposing a 56.2 mpg standard.  (This is the combined target, for both passenger cars and light trucks, unlike the previous numbers that I cited, which are just for passenger cars.  Sorry for the inconsistency.)  While this may seem like an insurmountable increase – cars must improve by 17.2 mpg in just 9 years! – it represents only a 0.8 gallon reduction in fuel consumption per 100 miles of driving.  Relative to the other CAFE regulations, that doesn’t seem so bad.

CAFE is a complicated – and dry – subject.  Which means “Part 2” of my dissertation on it will have to wait until later.  Stay tuned!

Categories: Fuel Efficiency, Policy Tags:

(Un)Fit to Print

July 1st, 2011 Comments off

The majority of folks these days get their news and information from some form of mainstream media outlet.  Which is a shame. Because, while most of us (myself included) assume “they must know what they’re talking about,” when it comes to subjects about which we ourselves have no expertise, it’s on those occasions when they so ignorantly cover a topic of which we DO have intimate knowledge that we then call into question their comprehension of basically anything.

I know stuff about cars.  Alex Taylor III does not.

In a June 27 Fortune Magazine online article (also published on, Alex The Third writes about how all the Chevy Volt enthusiasts out there are incredibly misguided because, although the Volt can travel an average of 35 miles on electricity alone, it only gets 32 mpg in the city (36 mpg highway) once the battery is depleted and the gasoline engine turns on.  The upcoming plug-in version of the Toyota Prius, on the other hand, can be expected to get 51 mpg city / 48 mpg highway (same as the current “regular hybrid” Prius) once its battery is depleted after 13 miles of electric driving.  Thus, Mr. 3 contends:  “On trips of 13 miles or less, the Prius plug-in and Volt deliver the same all-electric mpg: zero.  On trips between 13 miles and 35 miles in length, the Volt beats the Prius.  But after 35 miles, the Prius handily outscores the Volt.”

Unfortunately, Alex has failed to understand simple math. The actual cumulative fuel consumption of the plug-in Prius as compared to the Chevy Volt is shown below.  (I’ve used Taylor’s assumptions here, except for the 32/36 mpg that he cites for the Volt.  Although that’s what Popular Mechanics experienced, the EPA figure is 36/37 mpg, and since he uses the EPA figure for the Prius, we might as well be consistent.)

See, the Prius driver doesn’t suddenly overcome the Volt driver with respect to fuel saved at the 35 mile mark.  It takes quite a few miles of the Volt burning gasoline before the break-even point is reached.  In fact, one must drive 97 miles before any fuel-savings is realized by the Prius compared to the Volt.  Which is a lot more than most people drive each day.

But this isn’t even the full story.  I’ve driven both the Volt, and the plug-in Prius (in near-production form).  The architecture of the Volt lets you accelerate hard on electric-power alone.  It lets you reach triple-digit speeds with no help from the gasoline engine.  It has a true all-electric driving range of around 35 miles.  On the other hand, the plug-in Prius is largely the same as the conventional Prius, but with a larger battery.  The low power of its electric motor means that, if you press the accelerator more than just a little, the gasoline engine turns on.  Due to mechanical limitations of the motor-generator attached to the sun-gear of the planetary gearset in its power-split transmission, its electric-only speed is limited to 62 mph.  So if you’re on the freeway (and not stuck in D.C. traffic), the gasoline engine will turn on.  If you try to pass someone, the gasoline engine will turn on.  If you try to drive it at all like a normal person drives a normal car on a normal road, the gasoline engine will turn on.  The 13-mile “electric range” really isn’t.  This pushes the break-even mileage well beyond my generously calculated 97-mile mark.

Don’t get me wrong – the Prius (especially the plug-in version, which is not yet available) is a technically sophisticated, well-engineered vehicle that offers incredible fuel economy, with an internal combustion engine that is more advanced and efficient than that in the Volt.  And it’s true that the charge-sustaining MPG numbers for the Volt are somewhat disappointing (although that’s the penalty for lugging around a large 35-mile battery).  But Alex asserts – in Fortune Magazine – that the Prius is “a better idea” than the Volt, and that the numerous accolades the Volt has received are “an excess of praise in the wrong place.”

Which simply illustrates that he doesn’t know much about either car.