Is this a phenomenon outside of a few examples on the East Coast?
Of course, the most famous example of this was the abandoned section of PA 61 outside of Centralia (https://commons.wikimedia.org/wiki/Category:Abandoned_Pennsylvania_Route_61), but that was "decomissioned" when the private owner of the road covered it with dirt in 2020.
The closest example to me is a random back road in Ocean County, NJ where a short stretch is covered up with all sorts of tags. It probably more relates to an abandoned brick factory nearby in the Pineys which is also graffitied up. Photo of the densest part from a ride I did today:
(https://upload.wikimedia.org/wikipedia/commons/thumb/f/fb/Pasadena_Road%2C_Manchester%2C_NJ_graffiti%2C_July_2022_%282%29.jpg/640px-Pasadena_Road%2C_Manchester%2C_NJ_graffiti%2C_July_2022_%282%29.jpg)
There was another example I found Youtubing last night- it's an abandoned bridge north of Reading, PA:
https://www.youtube.com/watch?v=6p9gGQGsJqE
The recently paved approach to Rays Hill Tunnel on the Abandoned PA Turnpike also has tags all over it based on pics I saw.
The NJ example is the only one that is on an actively used roadway (albeit a lightly used one). Are there any other examples of such active roads tagged up?
Wards Ferry Road is the king of graffiti in California:
(https://live.staticflickr.com/65535/52100711882_30885b223b_4k.jpg) (https://flic.kr/p/2nnXLtU)IMG_8812 (https://flic.kr/p/2nnXLtU) by Max Rockatansky (https://www.flickr.com/photos/151828809@N08/), on Flickr
Krog St. underpass in Atlanta
(https://i.redd.it/a1cqxjnwc3ez.jpg)