Estes sometimes hires outside carriers to move truckload freight direct to the consignee. Usually these are the customers that take F O R E V E R to get you unloaded. I imagine the reasoning is, why should Estes pay their local guy his hourly pay to sit there when they can get one of the bottom feeder companies have their guys do it for free? More money in Estes bank account this way.
I know this an old post but I work for estes, and the Covenant drivers take the 53' trailers to the local terminals and the P & D drivers deliver them out. I also have spotted emtpy 53' trailers at shippers and returned later and picked them up full and brought them back to the terminal to be picked up by Covenant drivers.