MIT Study: Stiffer Roads = 3% better FE
 

I read an interesting article in Light & Medium Truck magazine that I thought I'd pass along:
Light & Medium Truck | Stiffer Roads Save Fuel, Study Says

It's a study out of MIT about the effect of road stiffness on fuel economy. Here' one except:

I once hit a (test ?) patch of very nice, smooth concrete on the London Orbital / M25 - instant fuel consumption dropped 10% right away (while on CC).

I buy that, I know going from asphalt to the chip seal stuff they put on drops 5-10% of my coasting range.

New asphalt can add 5% or more to my instant MPG.
Concrete is ok, but surface texture matters.

My best tank was done on long stretches of highway that were less then 3 months old.

gravel roads kill MPG
Dirt roads are better then gravel but still bad unless they are packed smooth then they can be better then asphalt.

quantified for big trucks by cummins a few years back

Relative Rolling Road Surface Resistance %
Concrete polished (best mpg) –12%
new baseline

Asphalt with finish coat 1%
medium coarse finish 4%
coarse aggregate 8%
Chip and Seal Blacktop (worst mpg) 33%

Road roughness can increase rolling resistance up to 20% due to energy dissipation in the tires and suspension (10% loss of mpg).


taken from p. 26 at http://cumminsengines.com/assets/pdf...whitepaper.pdf

Road surface roughness was something that I'd been aware of for some time,but what caught my attention about this study was that road stiffness matters. It's not just that the surface of the paving material itself is deflecting, but that the whole pavement is deflecting as your vehicle rolls over it. For example. it you were driving on a 1/2" thick plate of steel, the steel wouldn't compact or be rough, but it would bend as you roll over it, setting up a "wave" in front of you. Here's another excerpt:

So light vehicle weight is a good thing!

Yes, I would imagine the effect is more pronouced for heavier vehicles. Note that magazine is geared towards fleet managers of trucks up to Class 6 (26,000 lb GVWR)

That a hard surface is easier to travel across than a soft surface is something we know instinctively from jogging or cycling... but I've never thought about it in relation to driving, since that surface is still "hard" to those of us who don't weigh 2,000+ pounds. :D

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One of those: "D'oh, obviously" studies that is only obvious in hindsight. Fascinating stuff.

So, it would help us hypermilers to know which highways are concrete & which are asphalt. Where do we find those data, short of sampling every highway on our routes?

I might choose I-80 over US 50 for a weekend drive to Reno for a 3% gain in FE, but I'd need to know what each highway is paved with before starting the trip. I suspect the Interstate Highway system has pavement standards, but how much flexibility does each highway department have to choose its materials costs v. its labor costs?

This jives with papers I read from the 70s as well as material presented by Bridgestone for the trucking industry. Smooth concrete was the best.