CityEngine shapes are created like a tree with branches, once the shape is separated it is very hard to get it respond to the other shapes around it. Your sidewalks are separate shapes than your street because you are using the "built-in" street shape creation. Your UV splits are behaving exactly as they should. What you can do instead is make your street wider to encompass the sidewalks width, and before you split your sidewalks off into their own separate shapes using another uv split along the width, do your uv split along the length first. They will all be equal length that way, if I understand your request. This is just an idea, I have not tested it, but it wouldn't take long to write a quick code to test. However, without understanding the bigger context of your goals I cannot point to issues you might face beyond this. I would suspect that you need sidewalk creation on the intersections and that would be another issue to solve if you went this route. If you are trying to do this by sticking with the existing shapes, I don't have an idea yet.
