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A reference route is an unsigned highway assigned by the New York State Department of Transportation (NYSDOT) to roads that possess a signed name (mainly parkways), that NYSDOT has determined are too minor to have a signed touring route number, or are former touring routes that are still state-maintained. The majority of reference routes are owned by the state of New York and maintained by NYSDOT; however, some exceptions exist. The reference route designations are normally posted on reference markers, small green signs located every tenth-mile on the side of the road, though a few exceptions exist to this practice as well.
Reference route numbers are always three digit numbers in the 900s with a single alphabetic suffix. The designations are largely assigned in numerical and alphabetical order within a region, and designations are not reused once they are removed. Certain letters are avoided, such as
and "I" (used to indicate Interstate Highways and potential confusion with the number 1), "N" (used for institutional roads), "O" (potential confusion with the number 0), "R" (used for reservation roads), "S" (potential confusion with the number 5), "X" (a designation sometimes used in region 10), and "Y" and "Z" (at the end of alphabet and not used). "Q" and "U" are not currently being assigned due to confusion in the past. Designations are assigned as follows:

The first digit is 9, distinguishing the number as a reference route designation.
The second digit corresponds to the NYSDOT region number the route is in, with regions 10 and 11 using the digit 0.
The third digit is 6 for collector/distributor roads along limited access highways, 7–9 for parkways, and 0–5 for all other roads.An older system of reference route numbering used numbers ranging from 800 to 999 without an alphabetic suffix. Some reference markers with these older numbers still exist, even though these reference routes have new numbers. Every road maintained by NYSDOT also has a state highway (SH) number, used in state laws.

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