A new Expo Line plan to allow higher density residential development around five Westside stations may provide an important example of how to approach the city’s housing crisis, according to Paavo Monkkonen, associate professor of urban planning. “Look at how often a single-family home sells on a block. You’ll have a gradual change, not some crazy transition overnight,” Monkkonen said about the Exposition Corridor Transit Neighborhood Plan. “But we need some proof-of-concept model because it has never happened, really.”