Figure 2-11 Average Fuel Consumption as a Function of Speed
kilometre travelled—occurs at a speed of approximately 95 kilometres per
hour. The relationship between speed and fuel consumption is shown in
Figure 2-11 and illustrates a function with a minimum. Note that, once
again, at point A the slope of the curve is zero (because a tangent to the
curve at point A is horizontal), and so the marginal response of fuel
consumption to speed is zero.
Average fuel consumption falls and then rises as speed increases.
Average fuel consumption in litres per kilometre travelled is minimized at
point A at a speed of approximately 95 kilometres per hour (km/h). At
speeds less than 95 km/h, the marginal response is negative—that is, an
increase in speed reduces fuel consumption per kilometre. At speeds
above 95 km/h, the marginal response is positive—an increase in speed
increases fuel consumption per kilometre. At 95 km/h, the marginal
response is zero and fuel consumption per kilometre is minimized.