This study investigated potential road closure travel disruption due to climate change in two Portland watersheds. We used multiple models to develop an impact assessment method. Runoff was validated for 1988-2006 and used to estimate flood probability for 2020-2049. We surveyed streams at five crossings and found four bridges and roadways below the 100-year flood elevation, leading to frequent floods. Floods will become more frequent under some climate change scenarios. Vehicle miles traveled were not significantly affected by road closure, but vehicle-hours delay increased. Cost analysis is very sensitive to human fatalities or injuries and fairly insensitive to delays. This study presents a comprehensive classification of flood costs, identifies preventative measures, and makes recommendations. Results demonstrate the benefit of integrating top-down and bottom-up approaches in climate change impact assessment, and the need for spatially explicit modeling and participatory planning in flood management.