There are currently 16 U.S. Routes—14 mainline routes and two official special routes—that exist entirely or partially in New York. In New York, U.S. Routes are mostly maintained by the New York State Department of Transportation (NYSDOT), with some exceptions. U.S. Routes in New York are generally directly referenced by NYSDOT with their number; however, the letter "U" is suffixed to the number of the route on reference markers and in internal documents if there is numerical duplication between a U.S. Route and a state route. Two such numerical duplications exist: U.S. Route 2 and New York State Route 2 (US 2 and NY 2; inventoried as "2U" and "2", respectively), and US 15 and NY 15 ("15U" and "15").