How much diesel fuel does an idling semi use per hour?

An idling semi-truck can use anywhere from 0.5 to 1.5 gallons of diesel fuel per hour. The exact amount depends on the size of the engine, the age of the truck, and the condition of the engine. Idling is a major source of pollution for semi-trucks. Idling also produces noise and particulate matter, which can contribute to respiratory problems.