In my corner of PLSSia nearly all county roads have records indicating proof of the initial petition by the nearby landowners seeking creation of a farm to market road. The county commission would then send out the county engineer/surveyor to evaluate the feasibility of the project and consider possible damages owed to unwilling landowners along the path. Most of our documents list the path to be followed and the total width. In some cases, the middle of the road DOES NOT follow the section line or quarter section. For example, some 60-foot roads are 20 feet off of one landowner and 40 feet off of the other landowner. In rare instances the entire road may be off of one landowner. I've found one road that was laid out with the centerline beginning 30 feet to the east of a section corner and running south one mile to a point 30 feet west of the section corner, resulting in each landowner giving up the same amount of land but in a very long triangular shape.
There are statutory road widths that changed over the past 150 years. These only come into play for those roads for which the width was not stated in the road records. The earliest roads, by statute, were to be 66 feet wide.