What Counts as Highway MPG | Understanding Fuel Efficiency on Highways

When it comes to measuring vehicle fuel efficiency, two key metrics are often considered: highway MPG and city MPG. While both indicators serve to assess a vehicle's overall fuel consumption, they differ in terms of the driving conditions they represent. Highway MPG refers to the average miles per gallon a car can achieve while traveling on a continuous open stretch of road, typically at higher speeds and without frequent stops or starts. In contrast, city MPG represents the score a car attains on average within urban settings, characterized by frequent stopping, starting, and lower speeds. Understanding the distinction between these two measurements is crucial for consumers when evaluating a vehicle's fuel efficiency in both highway and city driving scenarios.

How Do They Calculate Highway MPG?

To calculate highway miles per gallon (MPG), the Environmental Protection Agency (EPA) employs a comprehensive approach. A significant portion of the EPAs highway MPG estimates is determined through a dedicated test cycle specifically designed for “high-speed” scenarios, reaching speeds of up to 80 mph. This test accurately assesses a vehicles fuel efficiency on highways and open roads, giving a reliable estimate of it’s performance under such conditions.

In addition to the high-speed test cycle, the EPA conducts three more tests that mimic different scenarios commonly encountered during city driving. These simulation tests replicate stop-and-go driving patterns, the extensive use of air conditioning, and operation in cold temperatures. By replicating these common scenarios, the EPA can assess a vehicles fuel efficiency in various driving conditions.

It’s important to note that these calculations are continually updated and refined to keep up with advancements in automotive technology and changing driving patterns. The EPA strives to provide the most accurate and up-to-date information to consumers, ensuring that their estimations reflect real-world scenarios. By calculating highway MPG in this meticulous and detailed manner, the EPA offers a standardized metric that helps individuals make informed decisions when purchasing vehicles and contributes to a more sustainable and energy-efficient transportation sector.

Differences Between Highway and City MPG Calculations

  • Highway MPG calculations are typically performed under controlled conditions on open highways, where the vehicle can maintain a steady speed without much traffic or stop-and-go driving.
  • City MPG calculations, on the other hand, reflect driving conditions in urban areas with frequent stops, traffic congestion, and lower average speeds.
  • Highway MPG tends to be higher than city MPG for most vehicles due to the consistent speed and lack of congestion on highways.
  • The EPA (Environmental Protection Agency) assigns an estimated city MPG and highway MPG rating to every new vehicle model based on standardized tests.
  • Actual MPG may vary depending on driving habits, terrain, weather conditions, and vehicle maintenance.
  • City driving typically involves more acceleration, braking, and idling, which can negatively impact fuel efficiency compared to highway driving.
  • In hybrid and electric vehicles, the difference between highway and city MPG is often more significant due to their regenerative braking systems and electric motors.
  • Fuel-efficient technologies, such as start-stop systems and aerodynamic designs, can improve both city and highway MPG ratings for vehicles.
  • Highway MPG is often used as a benchmark for long-distance driving or highway trips, while city MPG is a better representation of fuel economy during daily commutes and city driving.
  • Understanding the differences between highway and city MPG calculations can help consumers make informed decisions when purchasing vehicles and estimating their fuel costs.

The highway mileage test isn’t solely based on a constant speed. In fact, it combines the traditional highway test with a more rigorous assessment known as the “high speed” test. Lasting nearly 10 minutes, this test includes various accelerations and decelerations, including several uphill climbs from 0 mph to over 60 mph, culminating at a maximum speed of 80 mph. These additional factors are taken into account to provide a more comprehensive evaluation of a vehicle’s fuel efficiency on highways.

What Speed Is Highway Mileage Based On?

Highway mileage is based on a standardized test that combines various driving conditions to accurately determine fuel efficiency. These tests are designed to replicate real-world scenarios and provide consumers with a reliable measure of a vehicles performance on highways. One such test is the “high speed” or US06 test, which lasts for approximately 10 minutes.

During the US06 test, the vehicle undergoes a series of additional accelerations and slow-downs compared to the standard highway test. These additional maneuvers are meant to simulate high-speed driving conditions that drivers often encounter on highways. The most notable elements of this test include multiple climbs from 0 mph to above 60 mph, culminating in a top speed of 80 mph.

By incorporating these aggressive maneuvers into the test, manufacturers aim to evaluate the vehicles fuel efficiency and emissions under demanding driving conditions. This allows consumers to have a more accurate understanding of how the vehicle will perform during highway driving, where higher speeds and frequent accelerations are common.

The US06 test complements the standard highway test by covering a broader range of driving scenarios.


This parameter is especially relevant for assessing the car's performance at higher speeds and sustained driving. By understanding the distinction between highway and city MPG, consumers can make more informed choices when it comes to selecting vehicles that align with their driving patterns and requirements.

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