# Reduce Global Fuel Consumption by 75% Tomorrow By Cutting Speed in Half

That's what Kris De Decker over at Low-tech Magazine claims. He writes:

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

"Breaking speed records was an almost daily happening 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 velocities 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.

Air resistance (drag) increases with the square of speed, and therefore the power needed to push an object through air increases as 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).

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)."

Trains go too fast too.

De Decker goes on to stress that aerodynamics are important, but the key is speed. He even goes so far as to suggest that the French TGVs go to fast, consuming three times as much electricity as a conventional train. He concludes that "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. "

Questioning the Math

Regular readers know that this writer is a fan of lower speed limits. But one has to wonder- If we all drove everywhere at 35 MPH would it really save this much fuel? There has to be something wrong with his calculation, or the difference between fuel consumption in the city and on the highway would be far greater. I look for some comments here...::Low-tech Magazine
More TreeHugger on Slow Cars
The Inalienable Right to Speed
High Gas Prices = Fewer Auto Deaths
55 MPH: It's time to bring it back.
55 MPH Movement Is Gaining Speed
Our Radical Gas-Saving Tip: Drive 55 (or whatever the speed limit ...
Life Begins at Thirty ( MPH )

Tags: Oil