What does TH mean on an oversize permit?

Trunk Highway. Minnesota's name for a state highway: TH 61 is Trunk Highway 61.

Also printed as TRUNK.

On real permits

PrintedMeansState
Trunk HighwayA Minnesota state highway; MnDOT permits cover trunk highways, U.S. highways, and interstatesMinnesota
state trunk highwaysWisDOT's name for state highways; single trip permits cover interstate and state trunk highways onlyWisconsin

Decode a whole route line