Abstract Improved transportation systems is a key argument boosters offer local residents as to why they should support mounting a bid for the Olympic Games. Opponents argue that transportation improvement can and should take place without the mega-event and that a bid instead deviates resources away from necessary transport projects. Transport policy makers need a practicable understanding of how to make decisions under grand opportunities like the Olympic Games. I advance the theory under grand opportunities using Boston's transport planning approach for its bid to host the 2024 Olympic Games as a case study. Through an ethnography in Boston's bidding committee, content analysis of internal planning documents circulated among staff, and in-depth interviews with participants in the transport planning process, I analyze the reasons and process by which Boston 2024's Olympic transport proposal changed over time. I find that decision-making over transport emulated many characteristics of crisis; it was complex, risky, and occurred under high uncertainty. Once the initial bid was published, Bostonians demanded decisions for subsequent bid versions become transparent. Consequently, transport planners were forced to reduce complexity, to incur higher planning costs, and to discard projects beneficial for Boston's long-term development. I find that grand opportunities for transport were squashed over the course of Boston's Olympic bid. I conclude that grand opportunities move along a spectrum of high-low complexity during the decision-making process and thus propose to analyze this process with what I term the coincidental opportunism approach.

Highlights • Reviews literature on decision-making during crisis and grand opportunities. • Identifies attributes characterizing transport planning and policy during Boston's Olympic bid. • Finds that policy making in Boston reduced planning complexity, increased planning costs, and squashed grand opportunities. • Advances theory on decision-making under grand opportunities.