As part of the Traffic21 initiative at CMU, we are investigating the design and application of adaptive traffic signal control strategies for urban road networks. Our research has three broad themes: (1) development of signalization strategies that allow real-time response to shifts in traffic conditions (accidents, traffic dispersal at completion of major events), (2) low-cost deployment of advanced signalization concepts (implying strategies that work well with limiting sensing and methodologies for incremental insertion of adaptive signal technology), and (3) principled coordination of transit systems and personal vehicles through adaptive traffic signal control. We are currently using a microscopic simulation model of the Pittsburgh downtown road network as an experimental evaluation testbed.