The State Highway Commission shall adopt a manual and specifications for a uniform system of traffic-control devices for use upon streets and highways within this state. Such uniform system shall correlate with and, so far as possible, conform to the system then current as approved by the American Association of State Highway Officials, and the manual so adopted may be amended or revised from time to time as the Commission may deem necessary. The manual so adopted and any amendments or revisions thereof shall be published by the State Highway Commission and one copy thereof shall be distributed free of charge to the local governing bodies of counties and incorporated cities and towns.