With the calendar clearly marking the arrival of spring and the fast approach of Memorial Day Weekend, the unofficial kickoff of big summer vacations, the time of the year for the great American Road trip is upon us. The time honored tradition of packing up the family station wagon or your college roommate’s clunker car and hitting the open road dates back decades– with soundtracks of the drive evolving from the radio waves to cassettes all the way to mp3 players and streaming music through a smartphone app.

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Even in pop culture, generation after generation has had their road trips chronicled and memorialized: Grapes of Wrath during the Great Depression; the song Route 66 covered by a number of artists, including Nat King Cole and Chuck Berry, in the mid-20th century; the epic journey of the Griswold family to Wally World in National Lampoon’s Vacation in the early 1980s; Thelma and Louise getting up to no good in the early 1990s; the sophomoric humor of 2000’s Road Trip; and even Ted and Marshall of How I Met Your Mother reminiscing about their late 1990s road trips. While each successive generation can look back and wax nostalgic about their road trips and romanticize how other generations have no idea how it really was, is it possible to quantify which road trips got the most bang for their buck? As road trips have evolved, two key energy-related metrics have been tracked through the years: the average price of a gallon of gasoline in the United States and the average fuel efficiency of the American fleet of cars. While it is impossible to say whether a road trip across the country in 1980 was better or worse than one in 2000, these data do allow us to see what generation was getting the furthest on their dollar.

Data

The Energy Information Administration (EIA) is a great resource for all sorts of historical energy-related data needed for this analysis.

Gas prices

EIA’s annual data for U.S. regular retail gasoline prices goes as far back as 1992.  To go back further than that, EIA also provides historical retail motor gasoline prices in its Monthly Energy Review. This second source of data has prices for various types of gasoline (e.g., leaded vs. unleaded) and in different locations (e.g., on-highway prices vs. city prices). To make the analysis even more complicated, each data type is only available for a limited history (e.g., the standard data point of “Regular Motor Gasoline, All Areas” is only available from 1949 to 1990). For the sake of this analysis, we’ll pull the data for each year that is most representative of the prices of gasoline paid during that period:

• 1949-1975: Leaded Regular Gasoline, U.S. City Average Retail Price
• 1976-1977: Unleaded Premium Gasoline, U.S. City Average Retail Price
• 1978-1991: All Grades of Gasoline, U.S. City Average Retail Price
• 1992-2017: Regular Motor Gasoline, All Areas, Retail Price

Further, the values provided by EIA are in terms of actual dollars and not adjusted for inflation. So for the sake of a real comparison, we’ll also use the appropriate inflation factors to put those values in terms of the value of a dollar in 2009, as shown in the below graph:

Note that all prices EIA provides include tax paid by consumers. Note also that gasoline prices also have a significant regional variability, with certain parts of the country typically paying more at the pump than others– but this analysis is simply looking at the average gasoline price since road trips can and do stretch across every region of the United States. 

As you can see, most increases in the price of gasoline over the years have been tied to inflation (or, more accurately, inflation is also very tied to the price of gasoline that affects the price of all other goods and services in a modern economy). However, when someone who got their driver’s license in the booming 1960s or earlier talks about how much cheaper gasoline was back in their day, you can note that they were likely paying about the same at the pump that we’re paying today, and gasoline prices reached an inflation-adjusted all-time low in the late 1990s.

Fuel efficiency

EIA’s monthly energy review is once again the source to which to turn to grab historical data of the average fuel efficiency of the U.S. fleet of passenger cars. Again, this data set includes a variety of figures from which to choose, including light-duty vs. heavy-duty vehicles and short wheelbase vs. long wheelbase. Since we’re looking at the average road trip, we’ll use the light-duty vehicles with short wheelbases, which include data from passenger cars and light trucks/vans/SUVs more commonly driven by families. Also worth noting is the fact that the data here represent the average fuel efficiency of the fleet of cars for that year– both brand new cars consumers bought and cars that had been purchased years earlier that were still in operation. So while there are more efficient (and less efficient) cars available during all of these years, the data shown is for the efficiency of the average car you’re likely to pass on the freeway.

Note that 2017 data was not yet available at time of publication, so average fuel efficiency in 2017 was set equal to that of 2016. 

No adjustments needed for inflation here, just a rather pleasing trend showing the fuel efficiency of vehicles on the road increasing over the years. The drop in fuel efficiency from the 1950s into the mid-1970s is intriguing, but at the time oil seemed to flow endlessly and affordably and no one was fretting about air pollution or climate change so it can hardly be surprising to find that people were not too concerned with the miles per gallon they were getting. However right after the Arab Oil Embargo of 1973 when the dreams of endless oil security were burst, automakers clearly started to put a premium on minimizing dependence on gasoline (they were also prompted to do so by the nation’s first fuel efficiency standards) and the boom in fuel economies began, continuing through to the present day– both as a response to consumer demand and government regulation.

Crunching the numbers

The obvious next step is to combine these two sets of data by dividing the price of gasoline (in 2009 dollars per gallon) by fuel efficiency (in miles per gallon), resulting with the average cost of driving per mile for each year (in terms of 2009 dollars).

As is evident  here, the increase in fleet fuel economy has been the main driver in terms of how far a dollar will go on the summer road trips when looking at the overall trends. The increasing fuel efficiency standards and envelope-pushing technology of automakers has continued to make road trips more accessible and affordable for everyone across America.

However, looking at the particular peaks and valleys in the cost per mile chart, the price of gasoline is responsible for variations from the overall downward trend. The peaks in cost per mile in 1974, 1980, 2008, and 2011 all coincide with when the price of gasoline peaked (not coincidentally, these years also line up with years of recession in the United States). Likewise, the valleys of the graphs, when driving a summer road trip was the cheapest, coincides with the lowest gasoline prices over the 70-year history of price tracking.

Analysis and real-world implications

These numbers and graphs are fine, but they can sometimes be hard for contextualizing the actual difference in road trips. One way to visualize the change in fuel efficiency and gasoline prices over time is to compare how long of a road trip each generation over these 70 years could go on a fixed (inflation-adjusted) budget.

For a road trip route, nothing makes more sense than using the historic Route 66, America’s most famous road trip pathway. Route 66 was first imagined as an interregional link between Chicago and Los Angeles in the 1920s, becoming the migration route west that John Steinbeck proclaimed “Mother Road” in his 1939 novel Grapes of Wrath. Over the decades, Route 66 became less of a route than a destination in itself, known for its historic truck stops, tourist traps, kitschy diners, and natural landscapes. Today, drivers can still drive on pretty much the same path that the original Route 66 travelers would take, though it has largely succumbed to the interstate system rather than being one uninterrupted road.

If we take the most cost-effective year to take a road trip (1998 at just over $0.06 per mile) and price out how much it would cost to drive the entire length of Route 66, then we can see how far along the route you could get in every other year on that same (inflation-adjusted) budget:

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If the prices in 1998 allowed us to drive the  entire 2,448-mile length of historic Route 66 from Chicago to Los Angeles, then the price of gasoline and fuel efficiencies of cars both before and after that point mean most generations would not get nearly as far on the “Main Street of America.” Calculated this way, the $154 in gas money (in 2009 dollars) used in 1998 means other years are fairly limited in how far they can get:

• Flagstaff can only be reached for most of the 1990s, as well as 2001, 2002, and 2016;
• Santa Fe is only reachable for the stretch of 1987 to 2004, as well as 2009 and 2015 to 2017;
• Oil shortages, high gas prices, inefficient cars, and an economic depression all combined in 1980 and 1981 to be severe enough that this road trip budget wouldn’t even get you to Tusla.

It’s worth noting that this analysis is ignoring additional costs that come with the road trip, such as the cost to acquire and maintain a car in the first place, the amount you might spend on hotels, food, or roadside attractions along the way, the fact that you would be traveling at higher speeds later in the 20th century, and anything not directly tied to the price of gasoline and fuel efficiency. Those factors would surely influence the real planning of a road trip, but for the sake of the exercise of examining the costs and efficiencies of road travel over time, those external factors can be ignored.

So what are the real world implications of this analysis? What shapes these trends over time and why do they matter? Several important points can be drawn from these numbers that might inform the nation’s oil and energy future.

Carbon emissions

In terms of carbon emissions associated with these road trips, several factors come into play. First, the efficiency of a car is obviously critical to its climate friendliness, as the less gasoline needed per mile means there will be fewer emissions per mile of the road trip.

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Second, gasoline has become less emissive over time due to the requirements to blend ethanol into U.S. motor gasoline that started in 1990.  Ethanol is fuel made from corn and/or sugar, meaning it burns cleaner than oil-based fuels and is considered carbon-neutral because corn and sugar absorb carbon dioxide from the atmosphere as they grow.  The actual reality of climate and environmental friendliness of ethanol fuel is subject of much debate, as are the regulations surrounding ethanol. In any event, ethanol today makes up about 10% of U.S. motor gasoline by volume and, as such, a gallon of gasoline burned today is generally cleaner and less carbon emissive than a gallon of gasoline a few decades ago.

Lastly, the one way that price of gasoline ends up factoring into the carbon emissions of a road trip is with how accessible such a trip is as a vacation. History shows that the lower the price of gasoline, the more likely people are to jump in their cars and drive.  So, while lower gasoline prices are typically call for celebration, they also end up spurring increased vehicle miles driven and thus carbon emissions from the transportation sector.

Impact of gasoline prices

The point about the price of gasoline affecting people’s driving behavior is an important one for other reasons, too, as gasoline prices (and oil prices, more generally) touch every industry that relies on the transportation of goods and people, basically every industry imaginable. This process is shown to go both ways, too, as shown in the earlier discussion of how economic recessions and times of peak gasoline prices are intimately tied, so knowledge of the trends behind gasoline prices are important to monitor across the board.

Electrification of the fleet

While it has been and continues to be a slow process, the effect that gasoline prices have on industry and everyday life is another one of the main drivers of the electrification of cars, trucks, and transportation of any kind. The more quickly Americans can wean themselves off of oil products, the better they will be in the long run as they will be less vulnerable to oil price fluctuations and political posturing by oil-rich nations.

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Until electrification is achieved, the fragility of various industries to oil prices is also a major reason that the United States needs to continue with policies that protect Americans from sudden and unexpected oil price variations, namely keeping the Strategic Petroleum Reserve adequately stocked and ready in case of an emergency.

Fuel efficiency standards

Lastly, while electric cars are becoming more prominent in the market and are contributing to the overall gain in the overall efficiency of the U.S. fleet, the efficiencies of gasoline powered cars have been improving because of market forces, but also largely because of regulation. The Corporate Average Fuel Economy (CAFE) standards were first  set by Congress in 1975 (as a response to the 1973 oil embargo) and have been the chief driver of the improving fuel economy of cars on the road. While a portion of the customer base is clamoring for these improvements, regulations have really been the driving force to improving fuel efficiency and thus letting drivers get more bang for their buck at the gas pump. These fuel efficiency regulations have been recently targeted by the Trump Administration, as automakers have lobbied to have requirements relaxed in the coming years. While the decision to roll back these fuel efficiency regulations are up in the air as environmental advocates fight them and the debate is spilling into the court system, it is important to consider just how instrumental the fuel efficiency standards have been in getting the U.S. fleet (and their road trips) to the point they are today.

Conclusion

To tie a nice, neat box on this analysis of road trip fuel costs and what year got the furthest for the least cost, let’s see how the pop culture road trippers mentioned in the introduction faired:

• Grapes of Wrath (1939) and Route 66 (1946) Data don’t start until 1949, when the cost per mile (in 2009 dollars) was $0.16/mile
• National Lampoon’s Vacation (1983): $0.15/mile in 2009 dollars
• Thelma and Louise (1991): $0.09/mile in 2009 dollars
• How I Met Your Mother (flashback to 1996): $0.08/mile in 2009 dollars
• Road Trip (2000): $0.08/mile in 2009 dollars

So, while the generations crossing the country for their road trips in the earlier decades may still think their road trips were the best and most quintessentially American, it’s the late 1990s to early 2000s that served up the best deals for traveling by car. But with Elon Musk and others in the electric vehicle industry pushing the envelope of what’s technologically possible, who knows how long it will be before pop culture shows the first cross-country coming-of-age adventure using electricity and even renewable energy!

This article will be the first in a two-part series. In the next article inspired by the upcoming road trip season, we’ll look at how traveling the country by car compares with other modes of transportation (past, present, and future) in terms of energy use, carbon emissions, costs, speed, and more. Stay tuned for that follow-up post in the coming weeks!

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To see other posts taking deep dives into energy data, see this post on electricity demand during a federal government shutdown, this post analyzing economics issues surrounding clean coal, and this primer on how to use data from the Energy Information Administration. 

Sources and additional reading

1.8 Motor vehicle mileage, fuel consumption, and fuel economy

9.4 Retail motor gasoline and on-highway diesel fuel prices: Energy Information Administration

A Brief History of U.S. Fuel Efficiency Standards: Union of Concerned Scientists

Historic Route 66 Overview Map: Historic66.com

How Oil Prices Impact the U.S. Economy: Investopedia

Impacts of Higher Fuel Costs: Federal Highway Administration

Individual Year Conversion Factor Tables: Oregon State University

The History of Route 66: National Historic Route 66 Federation

Route 66: Road Trip USA

U.S. Regular All Formulations Retail Gasoline Prices: Energy Information Administration

About the author: Matt Chester is an energy analyst in Washington DC, studied engineering and science & technology policy at the University of Virginia, and operates this blog and website to share news, insights, and advice in the fields of energy policy, energy technology, and more. For more quick hits in addition to posts on this blog, follow him on Twitter @ChesterEnergy.