1. What is a TRL?

The TRLs are formal metrics that support assessments of a particular technology and provide the ability to consistently compare levels of maturity between different types of technologies. The TRL Scale uses a set of questions designed to measure progress of a technology toward maturity. The National Aeronautics and Space Administration (NASA) originally developed the concept of TRLs. Later, other Federal agencies, notably the U.S. Department of Defense, adapted the TRL concept.

The TRL Scale assesses the maturity of a technology in terms of certain characteristics, as measured by successful tests. The scale considers two aspects of the completed tests:

• How complete was the technology when it was tested? (Was it a paper-and-pen concept, a system of equations, a component, a subsystem, or the complete system?)
• How representative was the test environment?
  • Was it a computer simulation, a controlled laboratory experiment, a demonstration at a proving ground, or a real-world test?
  • How similar was the tester to the ultimate technology user? Was the tester the developer of the technology, another expert in the field, or a user with no more specific knowledge than the typical technology user?

Why Use the TRL Scale?

The TRL Scale focuses on completed tests and a typical testing progression toward technology adoption. Assessment panel members can use the scale to identify immediate next steps for a research or technology development project. Technical experts and program managers can use the TRL Scale as a guide to structure discussions about the state of development (or maturity) of a single technology. All parties to the assessment can reach a shared understanding of the technical state of the project by considering and debating the questions that comprise the TRL Scale. During its discussion, the panel can uncover technical gaps and questions that point toward next steps in the technology’s development. The discussion also helps to identify remaining steps and approximate the level and duration of effort needed to move a technology from its current state into deployment.

What Not to Do with the TRL Scale?

The TRL Scale focuses solely on the tests completed in the development of a technology, so the range of appropriate uses for it as an assessment tool is fairly narrow. The TRL Scale does not identify risks or challenges in technology development, such as:

• The difficulty of advancing the technology to the next level of readiness.
• The potential impact or benefit of the technology.
• The market for a technology.

Because of this limitation, assessors should include these indicators beyond the TRL when evaluating a project. The table below provides an explanation of the appropriate and inappropriate uses of the TRL Scale. Researchers must decide if the TRL Scale is an appropriate assessment tool for each technology product, as shown in table 1.

Understanding the TRL Scale

TRLs range from Level 1 (basic research) to Level 9 (implementation). To achieve a specific TRL, the technology must meet all of the requirements within that level and prior levels. Each level indicates a different measure of maturity and contains different requirements to determine the level of technical maturity.

The remainder of this section walks the reader through a description and requirements for each TRL and uses a real-world transportation technology example—Electronic Toll Collection (ETC)—to highlight the research maturity process of a set of technologies toward deployment. The TRL Scale has four categories: basic research, applied research, development, and implementation (figure 2).

The ETC Examples

Basic Research

The TRL Scale begins with basic research, as shown in table 2. For the case of ETC, the basic research focused on radio transponders. The precursor to ETC was radio-frequency identification (RFID) technology. Researchers developed radio transponders leading up to and during WWII. Military personnel used them to identify whether planes were Allied or enemy in an application called “identification, friend, or foe.”

Following WWII, patent applications in the 1950s and 60s identified ETC as a potential application for radio transponder technology, and economist William Vickrey proposed a hypothetical ETC system in The American Economic Review in 1963 (Vickrey, 1963). Still, there was no proof of concept until the early 1970s, when researcher Mario Cardullo developed a passive radio transponder with memory and demonstrated the concept to potential ETC users (Cardullo, 2003). The first three levels of the TRL Scale describe this kind of basic research. TRLs four and five capture the transition into applied research. Once TRL 5 is complete, research enters the development phase. Implementation marks a technology reaching TRL 9. The TRL Scale continues with applied research, as shown in table 3. A patent for automated tolling (figure 3) was awarded in 1971 (U.S. Patent and Trademark Office, 1971), as accessed through https://www.google.com/patents/US3602881.

Applied Research

TRLs four and five capture the transition to applied research. In the early 1970s, researchers at the Los Alamos National Laboratory began to develop and validate RFID tags for use in tracking systems for the U.S. Department of Energy—which was researching how to track nuclear materials—and the U.S. Department of Agriculture, which had the objective of tracking livestock (Violino & Roberti, 2005).

Throughout the 1970s and 1980s, laboratory research continued on RFID systems. As the technology matured and moved into development activities, Federal research led to the spinoff of private companies, such as Identronix and Amtech.

“The TRL Scale focuses on completed tests and a typical testing progression toward technology adoption. Assessment panel members can use the scale to identify immediate next steps for a research or technology development project. Technical experts and program managers can use the TRL Scale as a guide to structure discussions about the state of development (or maturity) of a single technology.”

Development

The TRL Scale is used to measure the development of a technology product, as shown in table 4. After TRL 5 is reached, research enters the development phase. In the 1980s, researchers tested early ETC prototypes on closed courses and public roads (TRB, 2016). As tests continued, the researchers replaced small temporary installations with larger deployments that had more readers and transponders. Limited vehicles (test, government, or commercial vehicles) used the systems during initial pilot phases. The public started using them after research proved them safe and effective.

Implementation

Implementation marks a technology reaching TRL 9. Researchers can use TRL 9 to measure a product’s implementation (table 5). For the case of ETC, early adopters of fully deployed systems included Texas in 1989 (North Texas Tollway Authority, n.d.) and Oklahoma in 1991 (U.S. Department of Transportation, 2016). As the years passed, more states tested and adopted ETC and extended the concept in various ways, including: open road tolling, standardized transponders, and high occupancy toll lanes. As of 2009, FHWA requires all new toll facilities with Federal funding to use ETC. Figure 4 shows ETC system in use at George Washington Bridge.