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Progress in efficiency–or lack thereof–in the automotive sector is huge indicator that the forces that be like us staying under 30 miles per gallon. For the last thirty years we have seen no real change in fuel economy despite the computer revolution. What a statistic! VW Rabbits in 1975 got 50mpg, and today GM touts that it has more products than any other manufacturer that gets almost 30. Progress?

Rod Adams

It is absurd to blame automobile manufacturers for producing big heavy vehicles if that is what their customers kept buying. Despite all opinions to the contrary, Americans are not lemmings - they make a lot of individual choices every single day.

I have no room to be smug about my fuel use since I "choose" to drive more than 40 miles each way to and from work and since I average about 25,000 per year when trips are included. I did, however, also choose to purchase a small, relatively low powered (90 hp) Jetta TDI that gets about 47 miles per gallon of diesel fuel in mixed driving. It is a relative of those rickety Rabbits mentioned above that is slightly larger, and safer with air bags and a bit more hip, shoulder and leg room.

I think physics is the limiting factor that prevents too much more improvement at the margins; improving the average will be the sum of a lot of individual decisions. Some people and professions will not be able to make the choice I made - it is very crowded if you try to carry more than 4 people in a Jetta and it would be pretty hard to be a plumber making calls with one.

Joe Willemssen

Actually, during every five year period from 1975, fuel efficiency has increased for both automobiles and light trucks -- with the exception of the latest period for light trucks, as so:

Vehicle type 75-80 80-85 85-90 90-95 95-00 00-04
Passenger car 13.9% 9.7% 16.1% 4.4% 3.7% 2.4%
Other 2-axle 4-tire vehicle 16.1% 16.8% 13.0% 7.3% 0.7% -7.1%


The reason the overall fuel economy average stagnated is because of a huge shift in fleet mix from autos to light trucks. From 1975-2004, automobile vehicle-miles (VMTs) per capita increased 21%, while light truck VMTs per capita increased at about 13 times that rate -- 270%. Since 1990, those numbers are 3% and 50%, respectively.

The ratio of VMTs of cars/light trucks was 84/16 in 1975 but stood at 63/37 by 2004. And since average MPG of light trucks is 6.2 mpg lower than cars, it has held the light vehicle average down.

Manu Sharma

The car I drive here in India already gives me more than 42Mpg. Maruti 800. It carries four people comfortably and it's the most inexpensive car in the country. For about two decades it was India's largest selling car.

It's also one of the most effeciently produced car in the world. It consumed a mere 280.6 Kwh of electricity and 0.103 MKCal thermal energy during its manufacture when I purchased it. Compare that with India's second largest car manufacturer, Hyundai Motors, that consumes 521.6 Kwh/car and 0.2812 MKCal/car. (Energy consumed during car manufacturing - should that be one of the criteria in the automotive X-Prize?)

If I install a CNG kit in my car (easily available in New Delhi where I live), it would give me an equivalent of well over 150 MPG. Which makes me wonder if X-Prize is aiming too low (at 100mpg).

Calculate yourself

Current Price of petrol: Rs.48/litre
Current Price of CNG: Rs.19.2/kg

Petrol Consumption for Maruti-800: 18km/litre
CNG Consumption for Maruti-800: 27km/litre

1 km/litre = 2.35214584 MPG

The CNG conversion kit costs Rs.36,000 which can be recovered in 1-3 years depending upon how much you drive. I'm seriously considering switching to CNG.


Maruti 800:

Maruti's Energy consumption:

Hyundai's Energy Consumption:

Ken Fry

I think your calculations are rather misleading, Manu. By running your car on CNG, you won’t change its fuel efficiency, you will change it’s cost of operation. (In the US, incidentally, the cost differential is much, much smaller: typically CNG costs about 15% less for the same caloric value. The economics don’t work well here, which is one reason why a small fraction of 1% of our fleet has been converted. Another is the weight of the tank, which lowers the fuel efficiency of the vehicle.) If I measure the cost of a fuel, then I can say that my first car (1966) got “the equivalent of” 200 mpg.

The 100 mpg proposed as a qualifier for the contest has nothing to do with fuel cost, but rather with the number of calories consumed. Coal is our cheapest fuel in the US, at less than ¼ the cost of gasoline per calorie. The intent of the X Prize is not, I certainly hope, to have us run cars on coal, which would give us the economic equivalent of 150 mpg. Imagine how much more quickly we’d suck up our resources then.

Most alternative fuels have only slight effects on “fuel efficiency” as we should be using the term here. Fuel efficiency should be measured as it is in the Shell Eco-marathon, in which each fuel is judged by its caloric value. Alcohols have low values, as does LNG. In fact, with both, you’ll use close to twice as much to run your engine. That doesn’t mean that your fuel efficiency has dropped, it simply means the caloric values are different. In all three cases (gasoline, alcohol, LNG) you are using similar amounts of our limited resources, in terms of their value as a fuel. You’ll create similar amounts of greenhouse gases.

During WW2, people ran their cars on wood, using gasifiers towed behind. It took a lot of wood to equal a gallon of gas. The wood was virtually free. So operating costs went down. On a cost basis, one could say these people were getting “the equivalent of 500 mpg” which would seem to suggest high efficiency. But the actual engine efficiency was unchanged in terms of calories in, hp out.

Manu Sharma

I agree, I was referring to cost rather than efficiency. But there are indeed tremendous benefits of switching to CNG - at least here in New Delhi India.

Apart from the lower cost of fuel, even the cost of converting a petrol based car to CNG-petrol hybrid is much less in India (beginning under $800) than US ($2000-4000). There are also far more CNG filling stations in Delhi than in US cities. So it's a great option.

On the emissions front, I'm told that: "compared to gasoline, CNG reduces exhaust emissions of carbon monoxide by 90 percent, carbon dioxide by 25 percent, and nitrogen oxides (NOx) by 35 percent." This is apparently even lower than E85.

Robert Melodia

There are ways to get around what is needed. The biggest obstacle is the ability to prevent the oil companies and oil countries from blocking what comes out. Once you are able to get around this the products will be sold quickly. I like this avenue because the PR/media coverage will prevent quite a few things from ending on the shelves of oil companies and never being seen again.


Actually, during every five year period from 1975, fuel efficiency has increased for both automobiles and light trucks -- with the exception of the latest period for light trucks, as so:

Garko Novis

buying gas has become a major investment decision, as in "do i invest in some food so i can get thru the day or some gas so i can get where i have to go?" It should never be this way but it is. But that doesn't mean we have to just suffer. There is a real solution in Water4Gas and you owe it to yourself to check it out! http://w4g4mpg.info

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