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The age of speed: how to reduce global fuel consumption by 75 percent

If we cut the average speed of all vehicles by half, fuel consumption would decrease by a whopping 75 percent.

Breaking speed records was an almost daily occurence throughout the 20th century. Cars, ships, planes and trains became faster and faster, year after year. Because the power needed to push …

If we cut the average speed of all vehicles by half, fuel consumption would decrease by a whopping 75 percent.

Breaking speed records was an almost daily occurence throughout the 20th century. Cars, ships, planes and trains became faster and faster, year after year. Because the power needed to push an object through air increases with the cube of velocity, this race to ever higher speeds raises energy consumption exponentially.

Engineers treat velocity as a non-variable, while in fact it is the most powerful factor to save a really huge amount of energy - with just one stroke, at minimal cost, and without the need for new technology. Lower speeds combined with more energy efficient engines, better aerodynamics and lighter materials could make fuel savings even larger. Picture : Mando Maniac

"The fastest car in the world reaches 10 times the speed of a normal vehicle cruising the highway, but it consumes 550 times more fuel"

Air resistance (drag) increases with the square of speed, and therefore the power needed to push an object through air increases with the cube of the velocity (see the formula here). If a car cruising on the highway at 80 km/h requires 30 kilowatts to overcome air drag, that same car will require 240 kilowatts at a speed of 160 km/h. Thus, a vehicle needs 8 times the engine power to reach twice the speed. In principle, this means that fuel consumption will increase fourfold (not eightfold, because the faster vehicle exerts the power only over half the time).

Picture: The Brooklands Society Photo Archives

Over a distance of 1,000 kilometres, the slow car would consume 375 kilowatt-hours (12.5 hours multiplied by 30 kilowatts) and the fast car would consume 1,500 kilowatt-hours (6.25 hours multiplied by 240 kilowatts).

Speed is the key

However, this extra fuel consumption can be diminished or even negated by, most importantly, more fuel efficient engines, lighter ~~vehicles~~ materials and better aerodynamics. Even though today's cars are faster than those from decades ago, they consume a similar amount of fuel. This is the reason why almost everybody is talking about energy efficiency and aerodynamics, and not about speed.

But if you lower the speed, fuel consumption is decreased by the full 75 percent. More efficient technology can not change that – unless in a positive way. If you combine a lower speed with more fuel efficient engines and better aerodynamics, fuel savings can become much larger than 75 percent.

Aerodynamics

Drag can be partly offset by better aerodynamics: a boxy car like the Volvo 740 has a drag area (drag coefficient multiplied by frontal area) that is almost twice that of the most aerodynamic standard car, the Honda Insight. The Volvo needs almost two times the engine power of the Honda when driven at 120 km/h.

"A boxy car vehicle at 60 km/h will consume much less fuel than the most aerodynamic vehicle driving at 120 km/h"

Picture : the Stanley - the fastest steamcar ever built.

Yet a Volvo 740 driving at 60 km/h will face less than half the drag and will need 4.6 times less energy power than a Honda Insight driving at 120 km/h. When compared to velocity, the potential of aerodynamics is limited.

Moreover, very good aerodynamics is incompatible with high speeds. Formula 1 racing cars have the worst drag coefficients of all vehicles on wheels, because of their large spoilers and very wide tyres. At higher speeds, it becomes important to minimize lift at the expense of better aerodynamics so that the car is not catapulted into the air.

Low speed trains

The blindness for the importance of speed leads to doubtful conclusions, like the environmentally friendly label of high speed trains. The French TGV that set the most recent speed record at 575 km/h for wheeled trains in 2007 has an engine output of 19,600 kilowatts. A contemporary “slow” train like the Siemens ES64 with a top speed of 240 km/h has a maximum power output of 6,400 kilowatts.

Travelling 1,000 kilometres, the “slow” train will consume 26,240 kilowatt-hours (over 4.1 hours) while the fast train will consume 33.320 kilowatt-hours (over 1.7 hours). A real slow train (like this one from 1956 with a top speed of 120 km/h) would consume only 20,000 kilowatt-hours over the same trajectory (and would do this in 8.3 hours, comparable to the travel time of a car).

"Technology can limit the growth of energy consumption, but if we want to lower energy consumption, we have no other choice but to adapt speed"

Picture: The Brooklands Society Photo Archives

The French high speed train is definitely more energy efficient than the Siemens locomotive, and that one is definitely more energy efficient than the 1956 train, because in both cases power consumption did not increase exponentially (*) with speed. But that does not take away the fact that the faster trains consume more energy than the slower trains. If, on the other hand, we would equip the 1956 train with the energy-efficient technology of today's high speed train, it would consume much less energy than it did 50 years ago.

Time is money

High speed trains are labelled environmentally friendly because they are not compared to other trains but to planes (A Boeing 747 would consume around 65,000 kWh over the same distance, over approximately 1 hour).

In a way this makes sense, because if a passenger prefers the fast train over the plane, he will consume less energy for a similar trip. He might not make that choice when the train would be much slower than the plane. On the other hand, if passengers that normally would take a slow train now prefer a fast train, high speed trains do raise energy consumption. The problem is that people see a shorter travel time as an advantage, while it has no ecological value whatsoever.

"Travelling from A to B would require twice as much time. But global world oil consumption would be halved"

Picture : Agence Eureka

You could as well argue that airplanes are green because they consume less fuel than rockets. This sounds ridiculous now, but if rocket planes take off, their inventors will no doubt claim that their toys are environmentally friendly because they go faster than airplanes but consume less than rockets. Technology alone can limit the growth of energy consumption, but if we want to lower energy consumption, we have no other choice but to adapt speed.

Fixation on technology

A decrease of 75 percent in fuel consumption is not peanuts. More than 60 percent of world oil production is used for transportation, which means that total oil production would be almost halved (-45%). In combination with more efficient engines, better aerodynamics and lighter materials a 75 percent reduction of oil production is not unrealistic.

Yet, when the International Energy Agency argues that the average car sold in 2030 would need to consume 60 percent less fuel than the average car sold in 2005, it claims: "With current technologies, only plug-in hybrids are capable of this”. This statement is wrong. We could lower the fuel consumption of cars (and other vehicles) by at least 75 percent, we could do it today, and we can do it with present technology.

© Kris De Decker (edited by Vincent Grosjean)

Article continues below:

Part 2 : breaking the hull speed and the sound barrier

Part 3 : the fastest "train" does 10,000 km/h

Part 4 : wind and human powered vehicles are setting speed records, too

Picture: The Brooklands Society Photo Archives

[]{#wavedrag}

[Wave drag, sound barrier and hull speed]{#wavedrag}

[]{#wavedrag} extreme high speeds, the link between velocity and power consumption becomes even more defined. Here, wave drag enters the picture and drag increases more. This is the reason why commercial airplanes never fly faster than an average speed of about 900 km/h (except for the retired Concorde). If they would go faster than 1.200 km/h, they would break the sound barrier at the expense of a massive increase in power consumption.

The Thrust SCC (pictured left), the car that holds the land speed record of 1,228 km/h, and thus broke the sound barrier, consumed 5,500 litres of fuel per 100 kilometres. So even though its speed is only 10 times higher than a normal car driving the highway, the supersonic car consumes around 550 times more fuel. A picture collection of land speed record vehicles can be found here.

When travelling on water, a similar effect comes into play - albeit at much lower speeds. Every watercraft contains a speed barrier that is (mainly) dependent on the length of the ship and on the shape of its bow. This barrier (called the hull speed in layman's terms) can be crossed, but only at the expense of another exponential increase in power consumption.

This is why ships are so much slower than other kinds of transport, and why most fast ferries were retired. The fastest watercraft reached a record speed of 511 km/h - not even half that of the fastest car. Underwater drag is even worse: the speed record of submarines is only 60 km/h.

[]{#rocketsled}

[Planes on rails : 10,000 km/h]{#rocketsled}

The fastest railed vehicle is not the TGV or the JR-Maglev, but an unmanned rocket sled that achieved a speed of more than 10,000 km/h. Rocket sleds are platforms on wheels, propelled by rockets and used to test missiles or (in earlier times) equipment for military aircraft. They do not use wheels but sliding pads which prevent the sled from flying from the track. The fastest manned rocket sled (pictured above) reached 1,017 km/h.

Some other remarkable manned rail vehicles were the American Pioneer Zephyr, the German Schienenzeppelin (which was powered by an airline propeller at the rear and held the speed record of 230 km/h for railed vehicles from 1931 to 1954) and the French Aérotrain (pictured above, source), a predecessor of the Japanese Maglev trains.

[]{#lowtechspeedrecord}

[Human & wind powered speed records]{#lowtechspeedrecord}

Human and wind powered vehicles are setting new speed records, too. The fastest human powered watercraft is the Decavitator (with a record speed of 34.3 km/h), while the fastest wind-powered speed record was set earlier this year by windsurfer Antoine Albeau, who reached 90.9 km/h (see picture above, taken from Masters Of Speed). That's only 5 times slower than the fastest engine powered watercraft. A windsurf board has a much higher speed barrier since it has a planing hull (unfortunately not an option for everyday use, see this video). See also: Sailrockets & kiteboats.

The speed record of a pedalled land vehicle is 86 km/h, that of a pedal powered aircraft 32 km/h, and that of a human powered submarine 15 km/h (only 4 times slower than the record speed of an engine powered submarine). The speed record for normal bicycles was set at almost 50 km/h (on average during a 1 hour run). The fastest wind powered car does 188 km/h.

Most of these vehicles are not suited for practical use, but that's not the point. They prove that speed kicks are possible without burning many barrels of oil. More information at the Human Powered Vehicle Association.

Speed records for manned vehicles 1900-2008

1900 : water (63 km/h), land (106 km/h), wheeled train (145 km/h), air (16 km/h)

1925 : water (141 km/h), land (235 km/h), wheeled train (210 km/h), air (448 km/h)

1950 : water (258 km/h), land (634 km/h), wheeled train (230 km/h), air (1079 km/h)

1975 : water (459 km/h), land (1015 km/h), wheeled train (331 km/h), air (3332 km/h)

2008 : water (511 km/h), land (1224 km/h), wheeled train (575 km/h), air (3530 km/h)Picture: a fighter jet breaks the sound barrier*

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by Kris De Decker
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