While driving along any state route in New York State, one will see small green signs such as the one shown above at the side of the road. These signs are called reference markers and denote your exact location in the state route system. They are located on all state routes, except roads maintained by the New York State Thruway Authority and sections of state routes multiplexed with county routes. There are also no reference markers on state routes within the City of New York that are not limited access. The signs have three lines of numbers and can be decoded as follows:
The first line of a reference marker contains the route number of the road that you are travelling on. If the road is an interstate highway, the number will be followed by the letter "I". Parkways and other state routes that do not have posted route numbers are assigned numbers called reference routes that appear in the first line of reference markers. A list of reference routes in the New York metropolitan area is available in the route listings section. Although service roads are assigned reference routes, the number of the main highway appears on the first line of the reference markers of service roads.
The second number is somewhat more complicated. The first digit identifies the region of the state that you are in. The region code for New York City is X and the region code for Long Island proper (Nassau and Suffolk counties) is 0. Westchester and Rockland counties are in Region 8. The second digit is the county code. The last two digits of the second line are the county order number. This will be 01 for the first county that the road passes through, 02 for the second, etc.
The third number is the mileage counter. Within each county, each state route is divided into one or more sections called control segments. The first digit of the third number is the number of the control segment. The last three digits are the distance in tenths of miles from the beginning of the control segment to the reference marker. The mileage counter always counts from south to north or from west to east, regardless of the direction in which the exit numbers increase.
