What is the speed limit when there is no posting (no signs)?
In New York State, the state speed limit of 55 mph is the legal limit if there is no posted speed limit. Details on posting speed limits in New York State can be found in the NYS Supplement to the MUTCD. However, there are two things to keep in mind.
One, drivers should still drive with reasonable care. In fact, a driver can still get a ticket for excessive speed for conditions.
Two, there may be a speed limit, but it just has not been posted or the signs have been knocked down. In New York State there are differences on how speed limits are set. The Vehicle & Traffic law discusses how each jurisdiction can set speed limits. For most highways in Towns and Counties, the speed limit is set by the New York State Department of Transportation.
New York State Vehicle & Traffic Law (See Titles 7 and 8)
New York State Supplement to the MUTCD (PDF) - see section 2B.13