Michigan Compiled Laws, Chapter 254. Bridges § 254.17

Sec. 17. The bridge specifications of the state highway department shall provide such requirements for load capacity, clearances, allowable unit stresses and loads, distributions, workmanship, impact and deterioration allowances as in the judgment of the state highway commissioner are necessary to meet the requirements of existing and future growth of traffic highway improvements and local needs. Such specifications may, at his option, be revised from time to time as he may deem best and shall be furnished free of cost to all proper parties requesting the same.