This is a classic "left hand not knowing what the right is doing". Management worries about idle time because of fuel usage. Automotive would probably have to replace less starter motors, probably less wear and tear on batteries, ignition switches etc. With diesels the turbos might last longer also.
local level management could care less about fuel usage or wear and tear on the equipment.
This whole "idle time" deal is simply a standard example of chasing a number. Someone in a cubicle in Atlanta with too much authority and too little common sense pulled a bright idea about reducing idle time out of his ass, and wrote a memo. He thought to himself "we will go green" so he decided in his infinite wisdom that we would reduce idle time by
x percent and he issued an edict to that effect. Everybody below him in the corporate chain of command is simply doing what we do best at ups, which is to mindlessly chase stupid numbers. The reality of fuel usage or wear and tear on the equipment means nothing; the only thing that matters is the number that shows up on the daily report.