N.Y. Comp. Codes R. & Regs. tit. 9, § 458.12 – Longitudinal placement.

(a) The placement of signs along the highway in relation to the roadway condition or regulation varies according to the type of sign used and the nature of the message conveyed.
(b) The following table indicates acceptable posting distances for the longitudinal placement of warning signs with respect to approach speeds under normal conditions on highways in rural districts:
85-percentile approach speeds Advance posting distance
Less than 25 mph 250 feet
25-35 mph 300 feet
35-45 mph 400 feet
45-55 mph 500-750 feet
(c) Signs should normally be erected individually, except where one sign supplements another or where guide signs must be grouped. Two signs for different purposes should not be located closer together than 200 feet if it can reasonably be avoided.