Steve really, really likes bridges. I've never met anyone else who knows or cares as much about bridges as he does. He likes looking at bridges, walking on bridges, learning about bridges, and watching bridges be built. We've walked across the Golden Gate Bridge together a couple of times, but we'd never walked across the Carquinez bridge, so that was perfect to add to the list of 40-4-Steve.
The new span of the Bay Bridge has a pedestrian path, so I'm sure that's in our future!