Tractors are rare in the expediting industry, because often times there's not enough freight to fill them. Expedite co.'s can easily fill a cargo van and half of a straight truck or part of a straight truck. it's mistakes on orders that are being filled, forgotten or badly needed freight, or extra freight that was not originally planned on. The difference primarily that I've seen is they're pulling very light loads, it's not unusual at all for a 53' trailer to have a quarter of a load on... or less. Teams are preferred, because they can find them more loads and run them further and faster and easier. Solo's not so much. Tractors are not utilized much in expediting simply because the space in that 53' wagon is really not needed all that much... where as the space in a cargo van/sprinter/cube/box van is utilized very well- as is the space in a straight truck. A straight truck is often more space than what is needed- but it's not too much more space.
Tractors don't sit that much because co.'s like to keep them moving to keep their options open with them and their capacity.
BBB