2006 Auto Show Fuel Economy

Here is a report from the 2006 New York International Auto Show talking about fuel efficient vehicles. We are now in 2010. The progress in the US towards higher fuel economy is very slow, in fact, until the major oil price spike in 2008 and the collapse of Detriot fuel economy was ignored by almost everyone except trucking companies.

Supercars Race for Fuel Economy

We have talked about the idea of replacing the traditional car race for the best time by races for the best fuel economy. Well, what would happen if you tanked up an Aston Martin DBS, an Audi R8, a Lamborghini Murcielago, a Ferrari 599GTB, and a Mercedes-Benz McLaren SLR will a gallon of gas each and ran them until they used the last drop? Who would go the farthest?

This video shows exactly that match up. The winner was the Audi R8, but it used a horrible 20 gallons per hundred miles (GPHM)! These cars may be super cars from the point of view of performance, but they sure do not save on gas!

Comparison of Fuel Economy Standards

All of the developed industrial nations of the world have government mandated fuel economy standards. These standards force automakers to produce vehicles with a certain minimum efficiency. In the United States, the relevant legislation is called CAFE or Corporate Average Fuel Economy. Detroit has long grumbled about CAFE and there is a body lobbyists who have tried (and are trying) to weaken the required efficiency. Looking around at the other nations, it is quickly seen that the US has very weak fuel economy standards. The report Comparison of Passenger Vehicle Fuel Economy and GHG Emission Standards Around the World in fact shows that the US has the weakest requirements of all. The chart above, taken from the report, shows that European, Japanese and Chinese vehicles are required to be considerably more fuel efficient than US cars.

This has permitted Detroit to fill the garages of the nation with gas guzzlers. This was not a large problem in the past era of cheap gasoline. But it has not prepared us at all for the dawning future of permanently high gasoline prices.

Aircraft Fuel Efficiency

Many fuel saving technologies have been deployed in the aviation world. In fact, aircraft have done a better job historically in seeking out ways to save on gas.

Airlines Get Better Fuel Economy Full

Airlines use a lot of fuel. But they also carry plenty of people over large distances. To discover how these factors interact we need to decide on a way to combine them. One way to do it is to look at how much fuel is used per mile per person. That is the same as the GPHM (Gallons Per Hundred Miles) rating for a car, but then we break that down by the number of passengers. As a large passenger carrying vehicle, be it airplane, bus or train fills up with passengers its fuel economy per passenger gets better. That is because with few passengers the engines still have to move the weight of the vehicle, which is almost all of it. Then as you add more passengers, the total weight to move goes up, but the portion of it represented by passengers also climbs. The overall result is less fuel spent per person.

For example, this chart on the Tupolev 154 shows the effect. As the load factor climbs to 100% the fuel used per passenger drops.



This is a basic and fundamental way to save on gas. We must look to modify the way we get around such as to keep vehicles running at close to full capacity. Do that and we will all save on gas.

Load Factor (%)	Passengers	Fuel Burned per Passenger-km (kg)
19	32	0.21
51	84	0.08
70	115	0.065
82	135	0.053
100	164	0.051

Gas Mileage At Altitude

Fuel injected vehicles have a computer that adjusts the amount of gas to match the oxygen in the air. That means even if the vehicle is operating at high altitudes where the air is less dense and thus has less oxygen per volume the computer will compensate with less fuel. So operating a fuel injected engine at altitude should not lead to a decrease in fuel economy through over rich mixtures. However, the reduced air density will decrease air resistance, especially at highway speeds. So if you are operating a fuel injected car at city speeds at altitude, you will probably experience little change in the gas mileage. If you are doing long highway speed cruises, you quite probably will see an improvement in your fuel economy.

National Fuel Economy Chart Vs Time

Ever wondered how the nation as a whole is doing with respect to fuel economy? The chart above shows the average fuel economy of the national passenger car fleet as a function of time. It is plotted in Gallons Per Hundred Miles (GPHM) versus the year. The raw data is available at the Bureau of Transporatation Statistics.

Remember that GPHM is the amount of gasoline the car uses for every 100 miles it travels. So to estimate the total gasoline used in the nation for a given year by passenger cars, you would have to multiply the number in the chart above by the total passenger car vehicle-miles for that year. The good news is that the chart shows a steady decrease. This is good because it means that each year the typical car uses fewer gallons to go a hundred miles. The bad news is that the curve seems to be flattening out. There was a big improvement in the 80's, dropping from more than six gallons per hundred miles to only five in 1990. But during the 90's up until the present day, it only dropped about another half gallon, to 4.5 gallons per hundred miles. Good that it is dropping, bad that the rate of dropping is getting smaller.

High Oil Prices and Airlines

Here is a guy who says that even oil prices up to $200 per barrel are not a problem for the survival of the airline industry. What do you think?

Super Lightweight Car

The more weight that a vehicle has, the more kinetic energy it needs to reach a given speed. Kinetic energy that is all lost again when the vehicle brakes to a stop. Weight reduction is one of the most important and effective ways to make a car more fuel efficient. The University of South Australia developed an ultralight car that has space for two people. The car has a mass of only 64kg, which corresponds to a weight of only about 140 pounds! Imagine that. In a normal car, almost all of the weight is just the car. In this case, the majority of the kinetic energy is going to move the passengers and not the car. And after all the point of a car is to move people, not metal.

This low weight was achieved by building the car using panels made of layered fiberglass and aluminum. These panels were used to build a basic box like shape. Then an aerodynamic form was constructed by layering styrofoam cut to an aerodynamic shape on top. A layer of fiberglass was then placed over the styrofoam to secure and protect it.

This is another example of a vehicle that would be perfect for neighbourhood driving or one person commutes. The heavy steel cars we drive are overkill for a lot of uses to which they are put. This overkill has a cost that shows up at the gas pump. Choosing the smallest, lightest vehicle that can serve a given function is one of the best ways to save on gas.

Freight Bikes

During the American golden age that followed World War II, plentiful cheap fuel and the spanking new interstate highway network ushered us into the rise of the personal automobile and “18-wheeler” trucks. As a result, every other method of transport was at least partly neglected. In that world, this made economic sense. But in a world of consistently high fuel prices it is not good to have all your eggs in one overpriced basket.

In a world of high gas prices it makes more sense to diversify transport. Each particular function served by transport can be more efficiently served by a specialized mode. For example, we have looked before at Neighbourhood Electric Vehicles and considered the use of a motorcycle instead of a much heavier and fuel hungrier vehicle. In the long distance point to point hauling of bulk freight specialized trains can be the most fuel efficient solution. And so on.

Freight bikes are bicycles designed to carry a light cargo over local distances. They are almost always tricycles, necessary for stability while loading, parking and unloading. Normally a large box or wire frame basket is attached to the front or rear. Special relatively heavy duty gearing is installed. The frame is also heavier and sturdier.

Although they seem symbolic of underdevelopment to many people, freight bikes are actually a very good solution in situations of fuel unavailability or high fuel price. Obviously their range and cargo load are limited by the human power source. It is also very difficult to operate them in hilly terrain. But for local delivery over flat ground they are perfect. I suspect that as the price of gasoline rises relative to labor we will see more and more of these on the streets of the United States. And if that helps us save on gas, it is a good thing.

Tractor-Trailer Fuel Economy

The trucking industry has paid a lot of attention to fuel economy. For them, their bread and butter depends on it. In fact, for them the word "performance" doesn't bring to mind high speeds or fast accelerations but rather good fuel economy per ton of cargo moved. Therefore looking at what they do to save on gas lets you take advantage of decades of tried and true tips and strategies. Caterpillar has published a report on Understanding Tractor-Trailer Performance which lays out the best ways they know to save gas with a big rig.

Their list of most significant factors affecting fuel economy includes these:

• Driver


• Route Selection


• Vehicle Speed


• Frontal Area of vehicle


• Aerodynamics of vehicle


• Hill Grade


• Climate


• Idle Time


• Tires


• Transmission

Caterpillar is very clear that the most important factor is the driver. The driver has direct control over many things including speed, accleration rate, usage of the brakes, shifting technique and time spent stopped with the engine idling. According to the report, fleets of identical trucks reveal fuel efficiency differences of 25% between the best and worst drivers. And even a bad trucker will probably drive more fuel efficiently than the average car driver. Truckers naturally develop a hypermiling culture amongst themselves due to the economic pressures in their industry.

The second factor they discuss is route selection. Caterpillar notes that driving in heavy traffic on congested roads notably increases fuel consumption. They find that a route of which 25% of the distance is congested leads to a 15% increase in fuel consumption. A route of which 15% is congested increases fuel consumption 8%. Roughly extrapolating to other percentages of congestion will allow you to estimate the mileage penalty of congested routes. In turn this lets you trade off the fuel penalties of distance and congestion. Choosing a longer route that avoids traffic could actually use less gas.

So Caterpillar is telling us that the most important factors determining your fuel usage and fuel economy are how you drive and where you drive. Read over the report if you have a few spare minutes. If it helps you save on gas, it will be time well spent!

Keeping an Eye on Traffic

The US Department of Transportation's Federal Highway Administration maintains a traffic monitoring program. Based on a network of some 4000 sensors on roads, streets and highways across the nation they can esimate the total number of vehicle miles driven in a given hour, day or month. Vehicle miles is a way of measuring a combination of how many vehicles were moving and how far they moved. One vehicle mile could mean a single car drove a mile or that 4 cars each covered a quarter mile. The graph to the side shows the traffic volume for the entire US averaged over a 12 month window. This is interesting, because the amount of fuel used by the nation principally depends on two things. One is how many vehicle miles we are driving and the second is how much gas it takes on average to move a vehicle a mile. This graph shows that vehicle miles traveled goes in one direction - up. Until the summer of 2008 that is. You can see how the $4.00 gasoline we had at that time caused an unprecedented crash in the amount of driving.

Four Reasons to Save on Gas

Why go to the trouble of learning hypermiling culture and buying fuel efficient vehicles? Well, here are four reasons why you might do just that.

Number one is the money you can save. Saving on gas means you will be shoveling out less cash each time you fill up. Remember when the price of gas was at $4.00 per gallon? Well, that can come back. Just because right now today the price is under $3.00 per gallon does not mean it will stay there. And if the price of gas soars having a fuel efficient vehicle can put a lot of money back in your wallet.

Number two is you can reduce the dependence of the nation on imported oil. The US now spends something north of $400 billion dollars a year on oil imports. That makes the nation very vulnerable to oil market moves. An increase in fleet fuel efficiency nationwide of only 10% would keep $40 billion dollars in the US economy. That is a lot of money.

Number three is peak oil. Petroleum is a non renewable resource. One day soon it will no longer be possible to increase the extraction rate. However, the demand for oil will almost certainly keep growing as the global population rises and developed nations like China and India increase their standard of living. That means we will enter into an era of permanently high oil prices. The less gas we use now, the more prepared we will be.

Number four is climate change. Using less gas will dump less carbon dioxide into the atmosphere. And dumping less CO₂ certainly cannot hurt the climate.

So start introducing yourself to hypermiling culture. You can help yourself, the nation and the world.

How to Measure Electric Car Energy Consumption

As the world begins a move to electric vehicles, we are working out how to quote their fuel economy. Remember when GM announced their new electric Chevy Volt was going to get 230 MPG? What they did was consider a trip of a certain length (set by the EPA fuel economy driving cycle test) and only count the gas used. Because the first part of the trip could use electricity from the battery, the first miles were "free" from the point of view of the gas tank. Of course that is very misleading, because the battery is still providing energy.

It looks like the EPA is going to regulate how automakers must report electric car fuel efficiency. I see that we are going to need it ... the automakers have already shown they are not responsible enough to manage this on their own. They have let the marketing department take the driver's seat and publish information that is not useful to consumers.

It seems that the EPA is still thinking about the best way to present electric car fuel economy data. One suggestion is to report two numbers: one giving the gas (normal internal combustion engine) fuel economy, and the other the energy use of the electric engine. At the root, I think this shows us that we should move away from thinking about gallons and towards thinking about Joules, the physical unit for raw energy. The most useful number would be energy used per distance traveled. In modern international scientific units this probably would be expressed in Joules per meter. It could be given as millions of Joules per 100 miles or something else a little more familiar to the American public.

At the end of the day what is being spent to move the vehicle is energy. In most circumstances the distance we want to go is the fixed given information. The natural measure combining these two is energy per distance traveled. Simple and it works for all types of vehicles: electric, hydrogen fuel cell or regular gasoline.

Could we Have Had Better Fuel Economy?

The average fuel economy of the US vehicle fleet is not very good. Sure, this is because until recently oil and gasoline were cheap like water. Now that is starting to change. With countries like China and India beginning to reach high standards of living the demand on global resources is set to soar. And at the same time, some of those resources are going past their peak, like for example oil. The result is that in the future fuel economy will be something to care about.

Look at this abstract and you can see that in the whole history of the automobile in the US, the fuel economy has been poor. I didn't buy the paper, so I am going to quote only the abstract below, but it gets the idea across. Also note that I converted the MPG numbers in the quote to GPHM, so it is not a straight quote.

This article documents and analyzes the changes in fuel efficiency of vehicles on US roads between 1923 and 2006. Information about distances driven and fuel consumed was used to calculate the on-the-road fuel efficiency of the overall fleet and of different classes of vehicles. The overall fleet fuel efficiency decreased from 7.14 GPHM in 1923 to 8.40 GPHM in 1973. Starting in 1974, efficiency increased rapidly to 5.92 GPHM in 1991. Thereafter, improvements have been small, with efficiency reaching 5.81 GPHM in 2006.

So the vehicle fleet considered en masse went from 7.14 gallons per hundred miles in 1923 down to 5.81 gallons per hundred miles in 2006. That is an improvement, but it doesn't seem like much considering that we are talking about 83 years. Of course in that time we added more weight to our vehicles, drove them at higher speeds and added all kinds of powered comforts like air conditioning. In fact, most of the technical advances in cars and trucks are in these other areas because fuel economy was never a concern.

But what if fuel economy had been a concern? Could Detroit have followed a different path and left us today with better fuel economy? I think the answer is yes, and so do other people. Here is a comment giving a list of changes Detroit could supposedly make to improve fuel economy by 40%. The list is copied here:

• Miller cycle
• variable valve timing
• variable displacement
• turbo-compounding
• NuVinci-style CV transmission
• lighter construction with composites and lighter metals
• smaller vehicles, designed for maximum utility

The next 7 posts here on Save on Gas will look at each of these technologies to see what advantages it could provide and speculate on why it has not been widely deployed by Detroit.

How Can GPHM (Gallons Per Hundred Miles) Help?

Using MPG (Miles Per Gallon) to measure the fuel economy of a vehicle can lead to some wrong impressions. It is not that there is anything wrong with MPG itself, just that it measures something that we don't normally use. Much better is to think about fuel economy in GPHM (Gallons Per Hundred Miles). Here is an example that shows how easy it is to be confused with MPG.

Assume you have a car that gets 10 MPG in the city and 20 MPG on the highway. Now this car goes on a trip that is 10 miles in the city and 10 miles in the highway. Over this 20 mile trip, what is the average MPG that you got? If you said 15 MPG you are mistaken. It looks like it should be 15 because 15 is the average of 10 and 20. But unfortunately MPG does not work that way. Let us see why not.

Over the first 10 miles in the city your car used 1 gallon of gas because it went 10 miles and gets 10 miles per gallon. Over the next 10 miles on the highway, you car used 0.5 or one half gallon of gas because it went 10 miles and gets 20 miles per gallon. This means your car used 1 gallon plus one half gallon or 1.5 gallons for the whole trip. The total mileage of the trip was 20 miles. This means the MPG for the trip was 20 miles per 1.5 gallons or 13.3 MPG! Not 15 MPG.

What happens if we use Gallons Per Hundred Miles or GPHM instead? To convert MPG to GPHM divide 100 by the MPG rating. The car gets 10.0 GPHM in the city and 5.00 GPHM on the highway. If we average 10 GPHM and 5 GPHM we get 7.50 GPHM. Is that the right answer? If we convert the 13.3 MPG we found before, it comes out to be 7.50 GPHM on the nose.

So you can average out GPHM ratings and you can't average out MPG ratings. This is a perfect example of why we would be better off using Gallons Per Hundred Miles (GPHM) and not MPG when we talk about fuel economy. GPHM works out like we expect, but MPG can be tricky and you can easily fool yourself.

Why does this happen? Well, it is because the two measures are thinking about taking different things as givens or fixed. With miles per gallon (MPG) you are thinking about using a fixed amount of gas and seeing how far you can go. The idea is to talk about the range you can get with a given amount of gallons.

With gallons per hundred miles (GPHM) you are talking about going a fixed distance and seeing how much gas it will use up doing it. Here you are talking about the fuel usage that it will take you to cover a fixed distance.

Now we can see the root of the problem when we try to use MPG for fuel economy. MPG assumes that you are going to use a fixed amount of gas and tells you about the different ranges different cars could get. But assuming you will use a fixed amount of gas is wrong. We want to go a certain distance. We don't say "I will drive until my car uses up 10 gallons." We say "I will drive to work (which is a distance of 10 miles away)." We should use GPHM to talk about fuel economy because the whole point of saving on gas is not to use a fixed amount of gas, but to change the amount and make it lower.

If you want to read more about this, I wrote about it before and the experts explain it really well here. As always, Wikipedia has useful information. And here is a handy calculator you can use to make conversions.