There are four cap parks currently in the works in Los Angeles.
From The Architect's Newspaper: According to Francie Stefan, community and strategic planning manager for the City of Santa Monica, no two freeway caps are the same. 'Some are glorified bridges, some need center supports, and some just span the whole distance,' she said. Structural design is influenced by whether you get support from outside walls or from center posts, and have mechanical or natural ventilation and lighting.
The largest and furthest along of the parks, the Hollywood Central Park project, would cover a wide swath over the 101 that currently cuts through residential neighborhoods."