Well these aren’t really artworks that are that hidden but not many people probably take too much interest in them.
At each of the waypoints you’ll find a set of traffic lights and at each set of traffic lights you’ll find the box that controls them. Instead of being the plain old blue all these ones have been painted with an artwork. What you need to do is to get the last number of the box, match the lettered pictures below with the ones on the boxes and substitute the numbers to find the cache co-ordinates. For example, if the box in picture A is number 1234 then A=4.
Parking might be an issue at some of the waypoints if you’re driving but you can sort that out.
The cache can be found at S FI GH.(E-H)(F-G)H E (I-F)(F+G)D IE.(A-G)(B-G)(E-H+C).
Checksums S 27 E 30.