Statistics are provided by the state Department of Transportation at the link here. There are figures for the whole length of specific highways (file 1), and total highway mileage by counties and municipalities (file 2).
The third file is for Traffic Volume Report by County. This includes interstates and state roads. There are several streets that one may not consider a state road but are considered as such by DOT. They are often designated by a three-digit route number, followed by a letter.
The Harlem River Parkway in New York County is 907D; most “parkways” are numerically designated. Old Route 16 in Erie County is 951V; many “old route” numbers have new numbers. Fort Drum Access Roads #1 and #2 in Jefferson County are 971Q and 971V, respectively; access roads and service roads are often noted numerically.
Even named streets are sometimes given route numbers. For instance, Wolf Road in Albany County is 910B. Albany Avenue in Ulster County has three different numbers, 981M, 983F, and 983G.
The fourth file is for Local Traffic Volume by County, broken down by town or city.
You will note that, while some counts are fairly recent, some are more than ten years old, especially the local ones. This is often a function of cost-cutting measures by municipalities.