Given the investment in streets, it is imperative for planners and urban designers to determine what makes streets social places. Defining street liveliness as stationary social behavior and duration of stay, we present an empirical longitudinal study extending previous research findings. Using observations and visual surveys, regression analysis and factor analysis, we study liveliness and determine its correlation with street characteristics. Extending prior findings, we ask, what changes in street characteristics over time predict increases in liveliness? Complementing previous results, we found liveliness was significantly predicted by increases in commercial seating, public seating, block variety, independent businesses, and community-gathering places.