Energy-efficiency loss occurs when more energy inputs are required to produce the same or reduced products or services. In reality, however, energy efficiency is difficult to measure. Because energy needs to be assessed relative to the amount of product or service provided, energy-use rates, commonly called energy intensities, are the measures ordinarily used to assess efficiency trends. Energy intensities reflect not only energy efficiency but also changes in other effects such as weather and extent of occupancy. However, the advantage of considering individual energy intensities is that you may easily measure and track them over time.
Energy efficiency is particularly difficult to measure in the transportation sector.
Participants in the workshop pointed out that EIA collects very little transportation data. EIA's transportation data covers only the residential sector. Therefore these data may not be available for future use. Value implications depend on who the customer is. Value judgements are inherent in every measurement decision, because one must define what measures what concept.