Determining Efficiency

Determining Efficiency

This report provides a comprehensive overview of the fuel and freight efficiency measurement and estimation methods used by the industry today. This will allow fleets to make better investment decisions, no matter the technology they are considering.

I want access to as much credible information as can be obtained, in order to determine the fuel savings potential for any technology that we may introduce into our fleet.

– Rob Reich, Senior Vice President, Equipment, Maintenance & Driver Development, Schneider National, Inc.

Overview and Test Methods

There are many fuel efficiency technologies available to fleets but no truck could or should have all of them. Fleets must analyze the range of options and compare them against their own operations to determine which offer the fastest payback. To do this, fleets need a solid understanding of their own operation and test data on the performance of various vehicle technologies.

However, it is not possible for fleets to test every device so they must rely on data from other sources. There are a variety of test methods and each has its appropriate application. Understanding what each test method involves, its benefits and challenges, and how it deviates from real world performance will help fleets have a better understanding of how to interpret the data.

OEMs should also conduct tests on the fuel efficiency of various components to help determine which technologies to offer on their vehicles. In addition, providers of technology should invest in testing in order to better develop and validate their designs.

Basic Test Methods

There are many published test methods, but all fall into one of five basic categories:

  • Computer Modeling—Computational Fluid Dynamics Analysis This method uses computer software such as facsimile digital geothermal models to calculate a vehicle configuration’s performance. .
  • Wind Tunnel Testing Tractor/trailer wind tunnel testing uses a physical scale model of a vehicle (or in some cases a full-sized vehicle) in a wind tunnel where environmental conditions can be controlled. The size of the wind tunnel dictates the size of the model needed.
  • Track Testing There are a variety of test protocols for use on a test track. Each attempts to quantify known components of the total performance and infer that what remains is attributed to the device being tested. Assumptions and simplifications can impact test results.
  • On-Road Testing This involves evaluating a tractor-trailer on an actual highway over a statistically significant number of miles with an acceptable level of repeatability. It measures the performance of the entire vehicle and all its factors as a net total.
  • Fleet Composite Evaluation All fleets perform fleet testing if they record miles driven, freight carried, and fuel purchased. This can validate technology choices when the data is collected and analyzed.


Determine How to Prioritize
All the test methods have value in helping to determine how to prioritize technology adoption.

A Starting Point for Technology Investments
Test results provide a starting point for discussion in technology investments.


Testing Variance
Variance among testing methods.

Extrapolation of test results.

Attributing Efficiency Gains
Need to precisely attribute efficiency gains.

Use of older data.

Precision vs. Accuracy
Confusion between precision and accuracy.

Complexity of Calculations
Complexity of calculations and variables measured.

Cost to Benefit Evaluation
There is no one single correct method for fuel economy evaluation. Each method has its costs and complexity. Cost to benefit needs to be considered before purchasing a fuel saving technology.

Case Studies

  • Aerodynamics The EPA documented one example of the variation in results from different test methods in its Regulatory Impact Analysis for Phase 1 Greenhouse Gas Rules.
  • 6×2 Axles A Trucking Efficiency Confidence Report published in December 2013 on 6×2 axles illustrates the difficulty inherent in comparing directly between test results rather than looking at trends.


  • The words accurate and precise are not interchangeable.
  • Data is available but needs to be shared.
  • The more methods used, the more confidence there is in trends.
  • Clarify objectives.
  • Adjust to operations.
  • Be comfortable with a range.


For Fleets

  • Understand scope, context, and constraints of test methods and how results will translate to real-word predictions.
  • Understand what factors are being measured, which are assumed, and which are estimated.
  • Accurately quantify the fleet’s own current performance.
  • Do not seek to determine absolute value for performance payback; instead look at the percent change.
  • Look for trends.

For Test Designers and Others Sharing Test Data

  • Achieve industry agreement on an absolute reference vehicle.
  • Initiate a concerted effort to correlate each test method to this absolute standard.
  • Continuously improve and refine measurement methods.
  • Share test results throughout the industry.
  • Work to provide better information on the potential impacts of real-word factors.