Hello, folks,

Here is a tool to help people save fuel while driving--

ROGERS TRANSPORTATION LAW

The following law came down to me just before I dozed off last night?

Δ gallons = - 1/30 (mph /mpg) (Δ minutes)

This simple relationship tells you how fuel consumed on a trip changes if you change your speed. If you adjust your driving to change the travel time by ?Δ minutes?, then the amount of fuel used will change by ?Δ gallons ?.

In simpler terms, suppose you want to get to your destination 30 minutes sooner. The amount of extra fuel used will be your travel speed divided by your miles-per-gallon. Conversely, if you lengthen the travel time by 30 minutes, the gallons of fuel saved will be the speed divided by your mpg. If you want to save more (or less) time, the amount of extra fuel will be proportionately more (or less).

Here is the way the formula looks for Europeans?

Δ litres = - 1/3000 (kph) (litres /100 km) (Δ minutes)

The formula is strictly true for small changes, and for a car where fuel consumption varies as the square of velocity. Notice that the formula does not depend on the length or duration of the trip. (Or when you initiate the action.)

Obviously, ?your mileage may vary.? This is a rule-of-thumb kind of formula, as anything applying to a complicated transportation system must be. Most people only have a rough guess for the ?mpg? anyway. Some may ask which speed to put into the formula. Probably the higher speed is best since most people will guess a little high on the mpg number.

The formula can be generalized to work for almost any mode of transportation. In which case, it might look like this?

ΔFuel = - n V (Fuel /distance) Δt

where fuel consumption varies as the nth power of V, and the formula is strictly true for small changes. An empirical choice for n might work best. Such could also be the case for an automobile, and then you would change the 1/30 constant.

Let?s say you travel about 70 mph, your car gets 25 mpg, and you slow down, lengthening the trip by 10 minutes. Here is your fuel saving?

Δ gallons = (10 /30) x (70 /25) = 0.93 gallons

So, how much were you paid for your time, at $3.75 per gallon?

0.93 x 60/10 x 3.75 = $21 /hour

And, you didn?t even have to work for it!

__________________