What are the requirements for breakaway hardware for sign posts on rural roads?
Sections 2A.19 and 2A.21 are the critical sections in the MUTCD for posts and mountings. Portions of the text from those sections is provided below. There is no modification in the New York State Supplement.
Essentially, if the sign is in the clear zone, it needs to be breakaway. There is a requirement from FHWA requiring all signs on Federal-Aid highways and any project using 3R monies must meet the requirements of NCHRP 350. Signs on other roads should meet this standard even if they are out of the clear zone.
The width of the clear zone will vary according to many factors, but if a car can hit the sign, it should be breakaway.
As for what hardware should be used for a breakaway application, there is a full list on the internet of all of the approved breakaway hardware available from the FHWA.
In addition, the NYSDOT Materials Bureau has an online list of approved materials for everything from signs to asphalt.
Here is the specific list for NYSDOT approved sign supports. Sign posts are included under the entry for "signs."
Acceptable devices range from simple spacer systems to omni-directional couplers designed for high speed situations. In some cases lightweight posts are acceptable without the need for a breakaway system. Whether a particular system is acceptable depends on the sign post weight and the soil type. In some cases a strong stiff soil is need to help the breakaway system shear at the right time. In other cases a stiff soil is not allowed.
In any case where a breakaway system is to be used, the maximum height of the lower post should be no more than four inches (4”) above the ground. Any taller and the post may snag a smaller vehicle and cause too much damage.
Section 2A.19 Lateral Offset
For overhead sign supports, the minimum lateral offset from the edge of the shoulder (or if no shoulder exists, from the edge of the pavement) to the near edge of overhead sign supports (cantilever or sign bridges) shall be 1.8 m (6 ft). Overhead sign supports shall have a barrier or crash cushion to shield them if they are within the clear zone.
Ground-mounted sign supports shall be breakaway, yielding, or shielded with a longitudinal barrier or crash cushion if within the clear zone.
Section 2A.21 Posts and Mountings
Sign posts, foundations, and mountings shall be so constructed as to hold signs in a proper and permanent position, and to resist swaying in the wind or displacement by vandalism.
The latest edition of AASHTO's "Specifications for Structural Supports for Highway Signs, Luminaries, and Traffic Signals" contains additional information regarding posts and mounting.
National Cooperative Highway Research Program (NCHRP) Report 350 Hardware Compliance Dates
Roadside Hardware Policy and Guidance (This page also contains links to NCHRP 350)