Why do big rig operators leave the engines going?
Some leave them on high idle to avoid that problem. Many buses also have a “fast idle” switch. The fuel consumption is somewhat higher at fast idle, but it works. They are also about to head out and drive for hours and hours at highway speeds (elevated engine temperatures) which will help to burn off what carbon has accumulated. Restarting the engine also causes wear because (a) oil is not well-distributed in the engine; and (b) the cold cylinder walls collect fuel which dissolves remaining lubrication. There is also lore and habit.
