A motorist unfamiliar with New York State's highways may have noticed and wondered about those small green numeral-laden markers placed at regular intervals along the roadway. Many will have realized that the top line of digits gives the route number, others that the bottom line appears to give distances, but what do the rest of the numbers mean? This page will explain in detail the purpose and meaning of these markers.

(This information has been compiled primarily from the Reference Marker Manual prepared by NYSDOT, and is here presented in condensed and (hopefully) somewhat clarified form. The Reference Marker Manual, being a government document, is understood to be in the public domain, although it is not directly reproduced here.)

These small signs, 8 inches wide by 10 inches high, are placed on all NYSDOT-maintained roads, including touring routes, reference routes, ramps, and so on. (Note that this does not include sections of city, village, town or county roads signed as state touring routes, nor roads maintained by other quasi-governmental authorities such as the NYS Bridge Authority.) They also exist on several parkways maintained by other State-level agencies or by the City of New York. They are sometimes referred to as Little Green Signs, or among the road scholars' community as TMM's (Tenth-Mile Markers). This latter term is not entirely accurate, as we will see. Their proper name is Reference Markers, and they are part of an extensive system devised by NYSDOT for identifying an exact location in the State's highway network.

Purpose of the system

The system was developed in response to the Highway Safety Act of 1966, which called for the states to develop a means of monitoring traffic and identifying high-accident locations along their roadways. The NYS Department of Transportation has expanded their use to include planning of maintenance and construction projects, as well as compiling a variety of physical inventories (traffic signals, railroad grade crossings, etc.). The DOT's Traffic Engineering and Safety Division maintains a database of all operative markers, including those actually placed in the field and those existing only on paper (such as on a city-maintained stretch of a NY touring route).

Placement of markers

Markers are placed at approximate tenth-mile intervals. On two-lane highways, they are placed on alternate sides of the roadway, facing the direction of travel. This means that on each side, markers are placed only every fifth of a mile, but between the two directions, all tenths of a mile are accounted for. On multi-lane highways, markers are placed on both sides every tenth of a mile "to avoid the temptation of crossing the highway in order to obtain the reference marker legend."

The standard tolerance for placing markers is ±0.01 mile from the true tenth-mile postition. This tolerance may be violated for several reasons:

1. At intersections, sidewalks or other obstructions, or where the shoulder is of hard rock or other impermeable material, markers may be placed as close as possible to their proper position, or they may be missing altogether. The missing marker is always accounted for in the overall sequence.

2. The ends of control segments (see next page for definition) are usually not within 0.01 mile of an even tenth-mile. In such cases, a tolerance of ±0.05 mile is used instead. Thus, the distance between the last marker of one control segment and the first marker on another control segment will be not less than 0.05 mile nor greater than 0.15 mile.

Example: If the last tenth-mile of a control segment is at 1.80 miles and the next control segment starts at 1.84, the marker at 1.80 miles will not be placed. If the next control segment starts at 1.94 miles, the marker at 1.80 will be placed but the marker at 1.90 miles will not.

3. On divided highways, one direction of travel is inevitably longer than the other. Since markers are placed from the south or west end of the route, increasing to the north or east end (this is known as the inventory direction), it is in this direction that the tenth-mile interval is most accurate. If the opposite direction is the longer alignment, its markers will be spaced at greater than tenth-mile intervals. If it is the shorter, they will be spaced at less than tenth-mile intervals. This way, identical markers are always placed directly opposite each other on divided highways.

4. Markers are often absent due to an accident, vandalism or maintenance work.