Yep, that memorandum jmdavis linked to is excellent. In addition to that but nothing official, here's a blurb from a group called Transportation Intermediaries Association where the third paragraph says that the type of freight might also make a difference in deciding whether reporting is required, where household goods are not classified as freight. This one from the IRS procedural manual for 1099 reporting, it is credit card payment reporting, but the table at .03 on page 5-6 shows that MCC 4214 motor freight carriers falls under 1.6041-3( c), which you probably already found. This has a broken link but gives food for thought about using 1099s as evidence that the payments are to independent haulers and not employees.