While page 4 of the document reads, with bracketed text by the Journal, “ASSIGNOR [the artist] hereby conveys, transfers and irrevocably assigns to ASSIGNEE [Caltrans] all of ASSIGNOR’s Copyright Ownership rights, title and interests in the Final Artwork,” those rights appear to return to the artist on page 6. There it reads, “ASSIGNEE [Caltrans] grants to ASSIGNOR [the artist], pursuant to this Agreement, a perpetual, exclusive, worldwide, irrevocable, sub-licensable, royalty-free license to use and exploit the Final Artwork, including in its Preliminary Works and final Material Object form.”
As to why the contract is necessary, Cochran further explained that aside from the need to repair and maintain the boxes, “the agreement also protects taxpayers from liability costs in cases such as a collision ruining a utility box, or, say Caltrans wants to post a picture regarding upcoming road work and there's some beautiful art in the picture, we can do that.” He also added that concerned artists can contact Caltrans for a detailed explanation of the contract and its purpose.