Do I really have to use chevrons and curves on every turn with a change in speed of 15 mph or more?
The original errata sheet of the CLRP Traffic Sign Handbook stated that there was a requirement for curve or turn signs on a corner if the advisory speed was at least 10 mph less than the speed limit and that chevrons or arrows had to be used if the advisory speed on a corner was at least 15 mph less than the speed limit. However, this is not true on all roads.
For those requirements to kick in the road must be a freeway or expressway, or classified as an arterial or collector AND have a traffic volume of 1,000 AADT or more. The actual text of the critical section from section 2C.06 of the National MUTCD is shown below. For roads with less 1,000 AADT or any road classified as a local road it is not a shall condition to put up these signs. However, it is still a good idea and studies have shown a significant reduction in crash rates when using curve signs with chevrons and arrows.
NYSDOT maintains a list of those roads classified as local. This information can be found on their website.
If you cannot find the classification of your road or are concerned about safety on a particular corner, you probably should plan on putting up curve or turn signs with chevrons or arrows.
Language from the 2009 National MUTCD
Section 2C.06 Horizontal Alignment Warning Signs
In advance of horizontal curves on freeways, on expressways, and on roadways with more than 1,000 AADT that are functionally classified as arterials or collectors, horizontal alignment warning signs shall be used in accordance with Table 2C-5 based on the speed differential between the roadway’s posted or statutory speed limit or 85th-percentile speed, whichever is higher, or the prevailing speed on the approach to the curve, and the horizontal curve’s advisory speed.
Horizontal Alignment Warning signs may also be used on other roadways or on arterial and collector roadways with less than 1,000 AADT based on engineering judgment.