 Future Caltrain and HSR service would utilize two underground levels, the lower of which would house the tracks and platforms, and the upper of which would house a retail concourse and waiting areas.Adjacent to the Transit Center and at the center of the redevelopment effort is a signature skyscraper at First and Mission Streets.The proposal featured plans from several major architecture firms including Skidmore, Owings & Merrill, Richard Rogers Partnership, and Pelli Clarke Pelli Architects.