Question

The data in Light-Duty Vehicles (1975–2006) show the efficiency of light-duty vehicles from 1975 (leftmost point of the connected line) to 2006 (rightmost point of the connected line). Each point represents a year in chronological order from the left end to the right.

Answer 1

Look at the graph carefully and answer the following questions:
• What generalizations can you make about changes in fuel efficiency (miles per gallon, MPG) over the course of the study?
• What generalizations can you make about changes in engine performance (horsepower) over the course of the study?
• What generalizations can you make about changes in vehicle efficiency (horsepower multiplied by MPG) over the course of the study?

Answer 2

Initially, mileage improvements were made by reducing power — the curve slopes downward to the right through 1982 or so. Then for a few years, mileage doesn't really get any better, but the power available improves, much like how Apple doesn't cut the price of each iPad model, but each year the same number of dollars buys you a more powerful iPad. In 1986, there's a significant jump of about 5% in the mileage. I wonder if that was due to a real improvement in engine efficiency or government regulation forcing automakers to get a higher average mileage and the automakers responding by making cars lighter? Don't know. After that, mileage slowly decreases, but available power greatly increases. I think this is automakers perceiving that the public still likes cars with some performance and as long as the gas mileage is decent, we'd rather have some more performance than a car that gets really high mileage but makes us fear for our lives merging onto the highway, etc.

Efficiency goes up dramatically between 1975 and 1982: in 1975, mpg*hp = 1750 or so, in 1982 it is up to 2200, a 25% increase! That's nothing, though, because from 1982 to 2006, it more than doubles!

Thanks for posting this question — I've had sort of a gut feeling that this had happened, but hadn't ever seen it so clearly illustrated!

Answer 3

no, thank YOU for answering :) yet again you've helped me out more than i could expect. thanks so much. i really really appreciate it