As gasoline prices approach $4.00 a gallon, we are tempted to think this is the highest price it has ever been. But in 1981 the average price was $1.35 and by many indexes that was much higher than today.
If we adjust that price by the CPI the 1981 "real price" is $3.24. But the average gas mileage of a car was 16 mpg in that year and is about 23 now. So the "real" price of gas (in 2010 dollars) to drive a mile in 1981 was 17.8 cents. If you divide $4.00 by 23 you get a price per mile of 17.3 cents. So by comparing the two periods using the CPI to deflate and price per mile seems about the same then and now.
The CPI is, however, not the best index for this comparison. (Go to the Relative Value of a U.S. Dollar to see a discussion of this.) It would make more sense to use the average wage or the average amount spent per household (what we call the consumer bundle). Under these two indexes, the "real price' was $3.62 and $3.92. These indexes give you a "real" price of gas (in 2010 dollars) to drive a mile in 1981 of 22.6 and 24.5 cents. This is 30% and 40% more expensive than the per mile rate at the current 17.3 rate of a $4.00 gallon of gas today.
Two more things that one should consider: The lowest federal income tax rate was 13.83% in 1981 and it is 10% today. And this year all wage earners are not paying their half of the social security tax.