What is the term for the operation of transport units using compressed natural gas?

The term "CNG service" specifically refers to the operational processes and activities involved in using compressed natural gas as a fuel source for various transport units, including delivery trucks. This terminology is widely recognized within the industry and denotes the specific services that involve the use of CNG for propulsion.

Using this terminology is important because it indicates not just the use of CNG as a fuel but encompasses all related services such as fueling infrastructure, maintenance, and regulatory considerations involved in the operation of CNG-powered vehicles. Each of the other options may suggest related concepts, but they do not convey the same level of specificity or industry standardization as "CNG service." This is why the answer reflects the accurate designation used in the field of transportation and energy delivery regarding the operation of vehicles powered by compressed natural gas.