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WTW analysis with four economies of sustainable automotive transportation finds CNG vehicles scoring highest

Joshua Gifford and Robert C. Brown at Iowa State University propose the evaluation of four economies in well-to-wheels (WTW) analysis of automotive transportation—primary energy consumption, GHG emissions, water usage, and cost of vehicle operation—in a paper published in the journal Biofuels, Bioproducts and Biorefining.

Life cycle analysis for automotive transportation, commonly known as well-to-wheels (WTW) analysis, has traditionally focused on greenhouse gas (GHG) emissions and primary energy consumption. Clearly, economizing on the use of primary energy sources and the amount of GHG emissions associated with automotive transportation are important sustainability metrics. Other important metrics are water usage and cost of vehicle operation.

No scenario is likely to simultaneously minimize all four metrics, suggesting the identification of a single figure of merit that encompasses all four economies of transportation fuels. We employed a normalization scheme that allowed calculation of a single composite score for each scenario called the CWEG (Cost-Water-Energy-GHG) score. Automotive transportation scenarios evaluated in this paper include a variety of fossil and renewable primary energy sources; several energy carriers as transportation fuels; and three distinct vehicle platforms including internal combustion engines, battery electric vehicles, and fuel cell electric vehicles.

The pair found that compressed natural gas scored highest, with CWEG scores of 71–74 out of a possible score of 100, well above the next highest score, which was 45 for conventional diesel hybrid electric vehicles. Fuel cell vehicles running on hydrogen generated using power from the US electric grid had the lowest CWEG scores, ranging from 13 to 15.


  • Gifford, J. D. and Brown, R. C. (2011), Four economies of sustainable automotive transportation. Biofuels, Bioproducts and Biorefining, 5: 293–304. doi: 10.1002/bbb.287



Kudos to the authors for considering water resources plus human caused atmospheric degradation. No mention in the post of the source of the natural gas. Also there is the question of infrastructure. Lastly, does Bill Gates think gas is cute?


"Fuel cell vehicles running on hydrogen generated using power from the US electric grid had the lowest CWEG scores, ranging from 13 to 15."

That says a lot, so CNG scores well and many have thought this was the case. Make the CNG vehicles hybrid and you may see even better results.

Big rigs as CNG/diesel/hybrid should score high as well. We have gone through a period where we have evaluated the alternatives, now is the time to implement the best ideas.


"Make the CNG vehicles hybrid and you may see even better results."

Blend in biomethane as the infrastructure developes and we'll see even MORE better results.


If you define biomethane as water treatment plants and feedlots, then you have to look at quantity, which is not even close. If you took all the biomass and digested it, gasifying it and making synthetic gasoline at $4 per gallon is more profitable than 40 cents a therm for methane.


Reminds me of the silly future city series where they talk about fuel cells but then for various reasons they gloss over they say its not gona work..

First off I dont see anywhere how they get the numbers exactly. I have seen far too many of these things use stupid math to get the results they want...

Secondly .. um exactly why would someone be using grid power to make h2 right now? You use grid power to charge an ev not to make h2. By the time people are making much h2 from grid power its assumed grid power itself wont involve much if any co2.

No the fact is the only way to get the deep cuts in co2 we will eventualy need we will have to convert over to bev and fuel cell cars and plug in cars.


Removing posts that challenge findings of two Iowa State students is cowardly and will not make GHG emissions a metric of value. It has no value because there is no substantial national or international action to mitigate man-made GHGs - due to the failure of the AGW campaign.

That said, wintermane is correct. Why not charge an EV with grid electricity? NW grids are mostly hydro. And would not an EV charged from PV qualify as zero-emissions?


I suppose you could say that it took fossil fuels to build the dam or make the solar panels, but that is the same as building an oil rig or a tanker ship. They all take fossil fuels to make.

That was and is one of my assertions, that one of the best uses of fossil fuels is to develop renewable energy resources. There is a gain and multiplier there that pays off every time we do it. If it takes 3 years to pay back the energy that went into making a solar panel, over the 30 year life we have an energy gain that we would not have gotten otherwise.

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