FHWA research led to guidelines regarding the percentage of streets and roads that should be in each of the functional classification categories. Different guidelines exist for urban and rural areas, because travel characteristics and density of development differs between the two land uses.

Percentage Guidelines Table

------------------------------------------------------------Percentage of Miles (range)

CATEGORY----------------------------------------------URBAN---------RURAL

Principal Arterials-------------------------------------- 5 - 10 % ----- 2 - 4 %

Principal Arterials plus Minor Arterials ------ 15 - 25 % ----- 6 - 12 %

Collectors------------------------------------------------ 5 - 10 % ---- 20 - 25 %

Local Roads-------------------------------------------- 65 - 80 % --- 65 - 75 %

All questions can be sent to: mdot-nfc@michigan.gov