We developed and tested a website and public display to connect and sustain carpoolers in the workplace. We arrived at this design through study of traffic congestion and its causes. After finding that many problems are deeply rooted in transportation infrastructure, we discovered several that could be addressed through design of an interface to carpooling. We found that people are often hesitant to carpool with unknown drivers. Our system offers numerous features to create and nurture sustainable carpools, bringing together design principles with organizational principles and workplace knowledge. Preliminary testing of our system encourages us that its combination of features could increase the success rate of workplace carpools. Keywords Design, community, social awareness, social reinforcement ACM Classification Keywords H5.2. Information interfaces and presentation (e.g., HCI): Miscellaneous.