On Coast to Coast, I heard them discuss the GPS tracking devices on big rigs. If the Carnes family or any police are reading this, I'd like to add a few ideas that weren't discussed on the show. I've never driven, but I did work in management for nearly a decade and have heard a lot of "tricks of the trade" from the drivers.
The GPS devices can be manipulated by the drivers and often are. I've heard of drivers putting metal buckets over those white round GPS transponders (or whatever they're called) up near the roofs of the cabs. Another thing that can be done is to go into the box on the side of the cab where gloves and such are often stored, and unplug the device. I've personally seen this done with Freightliner trucks using the Qualcomm tracking/messaging system.
Drivers do this for two reasons. The most common is to drive illegally, driving more hours than they're legally allowed to be on duty. After their hours and logbooks catch up, they plug it back in.
Another reason is to take a truck out of route unauthorized. This is usually done by drivers taking a load by their house unauthorized when their home is way out of route. After they get back onto the route, they plug it back in.
My former roommate, who had previously been one of my drivers, once told me a few years ago about how he once had a load going through Nevada and he unplugged his Qualcomm satellite locator in order to go WAY out of route to the Moonlight Bunny Ranch, a legal prostitution establishment in Nevada.
Someone could conceivably kill a person in their truck, then unplug their GPS tracking device, drive a long distance away to dump the body, drive back onto the scheduled route, and plug it back in.
One missing person who I didn't hear discussed on the show is Adam Blanchard. Please look at his thread in the missing people area of this website. There seems to be a possibility these two are related.
Adam Blanchard was staying at a motel in Ely, Nevada and went missing this spring just like Patrick Carnes. Two reasons I think they could be related are as follows. 1: Ely is off Highway US-93 which intersects I-80 in Wells, where Mr. Carnes was last seen. 2: Mr. Carnes told the cop he was tired and may have went to a motel. Obviously, he wouldn't have gone down to Ely and the motel where Mr. Blanchard stayed, but perhaps a perpetrator is jacking people at various motels in the region or even at rest areas or other places people could try to catch a nap.