Street Name (D3-1) signs should be installed in urban areas at all street intersections regardless of the route signs that may be present and should be installed in rural areas to identify important roads that are not otherwise signed.
On multi-lane streets that have a speed limit of 45 mph or greater, the lettering on ground mounted Street Name signs should be at least 8 inches high in uppercase letters and 6 inches in lower-case letters.
For local roads with speed limits of 25 mph or less, the lettering height may be a minimum of 4 inches high.
Supplementary lettering to indicate the type of street (such as, Ave, St, or Rd) or the section of the city (such as NW) may be smaller lettering at least 3 inches in height. Supplementary lettering should always use conventional abbreviations.