That's the point of the OP. For a variety of reasons, projects sometimes take exponentially longer than expected. It might only take a few days to paint some lines, to convert a car lane to a bike lake. But if the project instead means either making the sidewalk smaller, or expanding the road overall to accommodate the new lane, then timelines start growing. And, of course, a bunch of other improvements and maintenance are layered atop the project. Generally speaking, the road is brought also up to whatever safety standards have been changed. That might mean new sidewalk bits and pieces, new electronic signage or streetlights. Before you know it you are staring at traffic cones for years, mostly as the project waits for one or another subcontractor to do X or Y before Z can begin.