Driving costs haven't changed since the '50s

Driving costs haven't changed since the '50s

Long road trips are a classic part of American tradition. Time was, the whole family would pile into the Chevy or the Ford station wagon and hit the road on vacation.

The Big Crunch wanted to know: On a per-dollar basis, how are we doing compared to Americans of previous generations? Between fuel cost, fuel efficiency and inflation, who wins?

Heavy steel frames and inefficient engines meant those clunker cars ate up a ton of fuel, and gas companies grew into giant corporations feeding the nation's petroleum addiction. In 1956—the same year the Eisenhower Highway System was begun—American cars had an average fuel efficiency of 14.5 miles per gallon, according to data from the U.S. Energy Information Administration.

That means a 19-gallon Buick (NYSE: GM) Roadmaster (13.2 mpg) would have to tank up twice driving from Manhattan to Niagara Falls.

At 30 cents a gallon (the national average in 1956) fueling up would only cost $9.65. Making that same trip now in a 2014 8-cylinder Chrysler (: FCAM) would cost north of $60. That Chrysler makes about 23 miles to the gallon highway, which is right around average for the year.

But, you might point out that 30 cents in 1956 would buy you a lot more than it would today. Adjusted for inflation, that earlier trip to Niagara would cost you about $86 in 2014 figures.

It turns out that on a miles-per-dollar basis, we're pretty much in the same place we were in 1956. You could drive an average of 7.2 miles per dollar in 2014, up just 1.6 miles from 60 years ago. Of course, the average price of gas has dropped since the beginning of 2015—we'll see how far it drops and update the figures when new fuel efficiency numbers are available.

There was a big spike in miles-per-dollar figures through the 1980s and '90s—this economic efficiency peaked in 1998 over 14 miles per dollar in fuel. By 1998's fuel-economic standards, our trip to Niagara would cost just $29.50 in 2014 dollars.

Read More 6 Reasons Gas Prices Could Fall Below $2 a Gallon

But since then the cost of gas has increased dramatically and with it, our miles-per-dollar metric in recent years has dropped. Fuel prices, of course, are connected to geopolitical events and are far more volatile than average fuel economies in vehicles, so a miles-per-dollar figure has a lot more to do with the cost of gasoline than with fuel efficiency of the vehicles themselves.

That also means that fuel cost is the unknown variable—less control in this case means great volatility. But we do have control (to a certain extent) of the fuel efficiency of our vehicles, which is why you see the Teslas (NASDAQ: TSLA) of the world. One of the big selling points of driverless cars is that with complete automation, vehicles can travel in the most fuel-efficient way possible, using as much as 40 percent less fuel.

The issue comes in the use of miles-per-gallon as a measure for vehicle performance. The idea is that a gallons-per-mile metric would be more representative—and easier to compare between vehicles—than the current standard of miles per gallon.

In terms of fuel economy, the farther you go up the fuel efficient scale, the less of an effect a specific shift has. Switching from a car that gets 15 miles per gallon to one that gets 20 mpg (just 5 mpg more) reduces the gallons you need to drive to Niagara Falls by nearly seven—from 27.7 to 20.8. That makes a much bigger difference than switching from a car that gets 45 mpg to 50 mpg (the same shift), which is just 9.2 to 8.3 gallons.

This is where the math gets tricky, so pay attention. All "mpgs" aren't created equal: They matter more for clunkers than for super-efficient cars.

If the goal is to reduce the amount of fuel used by American cars, we should concentrate on bringing the lower echelons of the country's fleet up just a little bit rather than investing billions to make a few cars ultra-efficient.

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