Can I paint a single yellow stripe down the center of a highway just for guidance?
A single yellow line is no longer allowed to be used as a centerline marking. Section 3B.01 of the MUTCD covers Yellow Center Line Pavement Markings and it states:
“A single solid yellow line shall not be used as a center line marking on a two-way roadway.”

Chapter 10 in the Traffic Sign Handbook explains when and where center line markings should be used, but here is a quick summary.
Center line pavement markings are required:
- On paved urban arterials and collectors 20 feet or more in width with an average daily traffic (ADT) of 6,000 or more
- On paved roads with more than two lanes
Center line pavement markings are recommended:
- On paved urban arterials and collectors 20 feet or more in width with an average daily traffic (ADT) of 4,000 or more
- On paved rural arterials and collectors 18 feet or more in width with an average daily traffic (ADT) of 3,000 or more
Center line pavement markings are not recommended:
- On paved roads less than 16 feet in width without an engineering study due to the possibility of traffic encroaching in the opposite lane
The NYS Supplement does allow short segments of center line markings as an option (see text below).
Option:
On roadways without continuous center line pavement markings, short sections may be marked with center line pavement markings to control the position of traffic at specific locations, such as around curves, over hills, on approaches to grade crossings, at grade crossings, at bridges, and on approaches to intersections.
The proper marking is a double yellow line in those cases.
Before you remove an existing marking, be sure to document why you have done so and that doing so will not decrease public safety.
Resources
Traffic Sign Handbook for Local Roads, 2011 New York State Edition, September 2011 (pdf)
Section 3B.01 Yellow Center Line Pavement Markings and Warrants
Manual of Uniform Traffic Control Devices (MUTCD)
FHWA