I'm not sure if this is what everyone is referring to but on the INDOT website under on the Oversize and/or Overweight permits it lists the following:
When is a permit needed?
A permit is needed for the movement of a vehicle or a combination of vehicles, including the load, of a size and/or weight that exceeds the maximum legal size and weight limits as established by Indiana law [IC 9-20-3, IC 9-20-4]. Except for certain vehicles, which are given a permit exemption, any transport exceeding these limits must obtain a permit prior to moving on Indiana highways:
* Legal width limitation is 8 feet 6 inches.
* Legal height limitation is 13 feet 6 inches.
* Legal length limitation of a single vehicle operated under the vehicle's own motive power is 40 feet;
* Recreational vehicle is 40 feet.
* Common carrier of persons is 40 feet.
* Two-vehicle combination is 60 feet, with a 53-foot limit on the semitrailer. In addition, a semitrailer longer than 48 feet 6 inches may not be operated on any Indiana public highway when the distance between the kingpin and the rearmost axle of the semitrailer exceeds 40 feet 6 inches for semitrailers manufactured after December 31, 1984; or 42 feet 6 inches for semitrailers manufactured before January 1,1985.
* Three-vehicle combination is 65 feet, with a limit of 28 feet 6 inches for each semitrailer and trailer.
* Legal weight limitation of 80,000 pounds total gross weight, subject to all individual axle weights conforming to the Federal Bridge Formula.