(a) The commissioner of transportation shall develop uniform standards for directional signs erected under this chapter. The standards must provide for the size, lighting, spacing, design, colors, and maintenance of the signs. The standards must provide that:

1. (1) no pictorial or photographic representations be placed on the signs;
2. (2) directional signs facing the same direction of travel may not be placed less than one mile apart;
3. (3) signs located adjacent to an interstate highway must be within 75 miles of the described activity, and those located adjacent to other trunk highways must be within 50 miles of the described activity; and
4. (4) not more than one directional sign for the same activity and facing the same direction of travel may be erected along a single marked highway approaching the activity.