The only thing i can think of is that with an LTL move, you're hauling LTL freight, at a
highly discounted rate. The Expedite move -- are you talking about an MT (empty) move, here? -- probably pays 20 to 50 cents per mile, after the first 100 miles, which
almost offsets your fuel costs.
Since i'm really not sure that this is the answer to your question, i might suggest that you call and speak to someone at your company that can explain the difference -- nothing like the "horse's mouth!"
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Godspeed to all of you out there on the highways and byways!