Transportation Code §251.007

(a) The commissioners court of each county shall classify each public road in the county as a first-class, second-class, or third-class road. (b) A county may not reduce a first-class or second-class road to a lower class. (c) A first-class road must be not less than 40 feet wide or more than 100 feet wide. The causeway on a first-class road must be at least 16 feet wide. (d) A second-class road and a causeway on a second-class road must meet the requirements applicable to a first-class road. (e) A third-class road must meet the requirements applicable to a first-class road, except that: (1) a third-class road may be less than 40 but not less than 20 feet wide; and (2) the causeway on a third-class road may be less than 16 but not less than 12 feet wide.