You want a roof, build a roof. You want solar, build a solar farm. You should no more put solar over other structures than grow radishes up there. It's a terrible idea from every point of view (except eco-theatre).
That kind of frontier attitude "if we need more land we'll just build a longer road into the desert" won't fly anywhere within a thousand kilometers from where that bike path roof is built.
This method adds no land use. It also provides a roof for the users of the path.
Solar above car parks is great too -- it provides shade, means you don't get wet getting out of the car, and it provides energy.