In a 5-year study of the San Francisco Bay Area Metropolitan Transportation Commission, we found four planning styles at work: technical/bureaucratic, political influence, social movement, and collaborative. Each involved differing assumptions about knowledge, participation, and the nature of a good plan. Players using one style were often mistrustful or contemptuous of those working in others. Regional actionsas opposed to packages of projects for parochial interestswere rare. The few regional initiatives emerged from collaborative planning and social movements. We argue that where diversity and interdependence of interests are high, collaboration is the most effective approach. Key barriers to collaboration included state and federal funding formulas, earmarking, and the substantial documentation required by state and federal regulations.