When you’re considering a new vehicle, what’s the first number that comes to mind for measuring its economy? For many, it’s miles per gallon (MPG). However, as highlighted in the insightful TEDxDuke talk by Rick Larrick, relying solely on MPG can often lead to suboptimal decisions about car fuel efficiency. The problem isn’t just about reading the number; it’s about how our brains interpret and act upon that information. Fortunately, there are smarter ways to approach your vehicle-related energy decisions.
The core issue stems from a fundamental misunderstanding of how MPG works and how we, as humans, process numerical information. Instead of making purely rational choices, our intuitive minds often lead us astray. This article delves deeper into the principles introduced by Larrick, offering a roadmap to understanding true fuel efficiency and making decisions that genuinely align with your financial and environmental goals. We’ll explore why consumption metrics, clear objectives, relative comparisons, and expanded outcomes are far more powerful than the traditional MPG figure.
The Deceptive Nature of Miles Per Gallon (MPG)
For decades, MPG has been the standard metric for vehicle fuel efficiency in the United States. Mandated by the EPA in the 1970s, it’s prominently displayed on every new car sticker. Yet, its intuitive appeal masks a critical mathematical flaw that frequently misguides consumers. Larrick illustrates this perfectly with a thought experiment: which upgrade saves more gas – going from 10 MPG to 20 MPG, or from 20 MPG to 50 MPG?
Most people instinctively lean towards the 20 to 50 MPG jump. It represents a larger numerical difference (30 MPG vs. 10 MPG) and a significant percentage improvement. However, this intuition is wrong. The 10 MPG to 20 MPG upgrade saves nearly twice as much gas. Why the disconnect?
The relationship between MPG and fuel consumption is curvilinear, not linear. This means that improvements at the lower end of the MPG spectrum (e.g., from 10 to 20 MPG) yield far greater gallon savings than similar or even larger MPG increases at the higher end (e.g., from 30 to 40 MPG). Here’s a breakdown over 100 miles:
- 10 MPG to 20 MPG:
- At 10 MPG, you use 10 gallons per 100 miles (100 miles / 10 MPG = 10 gallons).
- At 20 MPG, you use 5 gallons per 100 miles (100 miles / 20 MPG = 5 gallons).
- **Savings: 5 gallons.**
- 20 MPG to 50 MPG:
- At 20 MPG, you use 5 gallons per 100 miles.
- At 50 MPG, you use 2 gallons per 100 miles (100 miles / 50 MPG = 2 gallons).
- **Savings: 3 gallons.**
As you can see, despite the seemingly larger improvement, the 20 to 50 MPG change saves less fuel. This counterintuitive truth highlights the need for a different perspective when evaluating gas mileage.
Behavioral Economics: Understanding Our Decision-Making Flaws
Our tendency to misinterpret MPG is a classic example of a cognitive bias, a concept deeply explored by behavioral economics. This field, which emerged from the convergence of psychology and economics, acknowledges that humans are not always rational actors. Nobel laureate Daniel Kahneman, a pivotal figure in this discipline, introduced the concept of “What You See Is All There Is” (WYSIATI). Essentially, we get trapped by the information presented to us, struggling to convert it into a format that truly reflects our underlying concerns.
For car fuel efficiency, this means we see MPG, and our brains try to operate within that framework, even when it’s misleading. We default to simple arithmetic rather than the inverse calculations required for accurate consumption assessment. Recognizing this inherent human limitation is the first step toward building better information systems and making superior energy decisions.
The CORE Principles for Smart Energy Decisions
To counteract our biases and make truly informed choices about vehicle fuel efficiency, Larrick proposes four CORE principles:
1. Focus on Consumption Metrics: Embrace Gallons Per 100 Miles (GPM)
The most direct solution to the MPG illusion is to shift from efficiency (miles per gallon) to consumption (gallons per mile or, more practically, gallons per 100 miles, or GPM). GPM provides a linear and intuitive measure of how much fuel you’re actually using. If you compare two vehicles side-by-side using GPM, the difference in gallons consumed directly reflects the fuel savings over a given distance.
Consider the previous example in GPM terms over 100 miles:
- A 10 MPG car uses 10 GPM.
- A 20 MPG car uses 5 GPM.
- A 50 MPG car uses 2 GPM.
The difference between a 10 GPM and 5 GPM car is 5 gallons per 100 miles. The difference between a 5 GPM and 2 GPM car is 3 gallons per 100 miles. This clarifies the true savings immediately. The EPA recognized this in its 2013 redesign of vehicle labels, now including GPM as a key metric.
2. Know Your Objectives: Beyond Just Gas
Ultimately, people don’t care about MPG or GPM for their own sake. They care about their underlying objectives: saving money (cost) and reducing their environmental footprint (environmental impact). When information is presented in a way that directly addresses these objectives, people are far more likely to act on their true preferences.
A study mentioned in the talk demonstrated that when consumers were shown greenhouse gas emissions ratings alongside traditional fuel cost, they became more sensitive to their existing pro-environmental attitudes. This “signpost effect” reminds people of their goals and provides the relevant data to achieve them. For instance, knowing that a certain car emits X tons of CO2 per year makes the environmental impact tangible, unlike an abstract MPG number.
3. Value Relative Comparisons: Context is Key
Numbers often lack meaning in isolation. We struggle to grasp whether “163 therms of natural gas” is good or bad without a benchmark. This is where relative comparisons become invaluable. Comparing your energy use to that of your neighbors, as pioneered by companies like Opower, can be a powerful motivator.
Opower’s success lies in taking social psychology research and applying it to utility bills. By showing you how your energy consumption stacks up against your “average” and “most efficient” neighbors, it provides immediate context. This isn’t just about guilt; it leverages social norms and gives clear goals. If your neighbors, living in similar homes in the same climate, are using significantly less, it prompts you to investigate your habits and find ways to improve your own energy consumption.
4. Expand Outcomes: Think Big Picture, Long Term
Our decisions are often swayed by how information is scaled. Small, immediate differences can seem insignificant, while larger, long-term impacts tend to grab our attention more effectively. The cell phone plan example vividly illustrates this point:
- A difference of 2.3 dropped calls per 100 (4.2 vs. 6.5) and $60 per year might lead people to choose the cheaper plan.
- However, framing it as 23 dropped calls per 1,000 (42 vs. 65) and $5 per month makes the quality difference seem more substantial, often swaying people towards the higher-quality, slightly more expensive option.
Applied to car fuel efficiency, this means moving beyond gallons per 100 miles to considering the lifetime impact. Instead of thinking about saving 1 gallon per 100 miles, consider saving 1,000 gallons over 100,000 miles (a typical car lifetime). The thought of burning an extra thousand gallons of fuel, and paying for it, suddenly makes the decision much more impactful and easier to act upon for cost savings and environmental impact.
The Redesigned EPA Label and Practical Tools
Recognizing these principles, the EPA significantly redesigned its EPA label for new cars in 2013. While MPG remains, it is now complemented by more actionable data:
- Gallons Per 100 Miles (GPM): A direct consumption metric, offering a clearer picture of fuel use.
- Annual Fuel Cost: Translates fuel efficiency directly into a financial objective, making the cost impact tangible.
- Greenhouse Gas Ratings: A visual representation of the car’s environmental footprint, serving as a ‘signpost’ for those prioritizing ecological concerns.
- 5-Year Fuel Cost Comparison: This clever addition combines several CORE principles. It offers a relative comparison to an average car, scaled over a significant period (five years), to show the expanded outcome of owning that specific vehicle. This number can quickly show thousands of dollars in savings or extra costs, making the decision’s impact undeniable.
Beyond the car sticker, tools like gpmcalculator.com (developed at Duke) empower consumers to make personalized comparisons. By inputting MPG values for different vehicles, expected driving distance (consider a lifetime like 100,000 miles!), and an estimated gasoline price, you can directly compare true car fuel efficiency and cost differences between models. This allows you to apply the CORE principles directly to your car buying decisions, moving past the misleading allure of MPG and towards decisions rooted in actual consumption, costs, and long-term impact.
Fueling Your Knowledge: Smart Efficiency Q&A
What is the main problem with using MPG (Miles Per Gallon) to understand car fuel efficiency?
Relying solely on MPG can be misleading because improvements at different MPG levels don’t save the same amount of fuel, making it hard to see true gas savings.
What is ‘gallons per 100 miles’ (GPM) and how is it different from MPG?
GPM measures how many gallons of fuel a car uses to travel 100 miles. Unlike MPG, GPM provides a direct and linear understanding of actual fuel consumption and savings.
Why is GPM considered a better way to compare car fuel efficiency than MPG?
GPM gives a clearer picture of how much fuel you actually consume and directly shows the difference in gallons saved between vehicles. This helps you make more accurate decisions about costs and environmental impact.
How has the EPA (Environmental Protection Agency) updated car labels to help buyers?
The EPA redesigned new car labels to include ‘gallons per 100 miles’ (GPM), annual fuel cost, and greenhouse gas ratings. These additions make it easier to understand a car’s true fuel consumption and environmental impact.
