Motivated by climate change and increasing emissions from the transportation sector, government initiatives aim to shift travel away from automobiles to other modes such as bicycling. Despite broad agreement that high-quality infrastructure is critical to attracting and safely accommodating active travel, current design procedures for bicycle facilities lack evidence-based grounding of fundamental design parameters that are critical for user safety, such as perception-reaction time (PRT) and deceleration rate in stopping sight distance calculations. This research aims to measure the perception-reaction time and deceleration rate for bicyclists reacting to a fixed object in unexpected braking scenarios. Bicyclist PRT and braking behaviours were measured across two samples: (1) an unexpected response trial (n=52), and (2) an expected response trial (n=250). In the unexpected trial, participants rode around a course on an instrumented bicycle, and their braking response to an unexpected hazard was measured using a strategically placed video camera. In the expected trials, participants rode toward a manually-controlled traffic signal, and were told to “come to a full stop as quickly as possible, safely” once the light changed from green to red. Regression models were estimated to determine predictors of PRT, deceleration rate, and overall stopping distance. We found that the 85th percentile unexpected PRT was 0.84 seconds, substantially lower than previously observed in motor vehicle studies, possibly due to heightened vigilance when riding a bicycle. Based on these results, the current design guidance of 2.5 seconds appears to be conservative for use in bicycle facility design. However, the 85th percentile deceleration rate was found to be 0.20 g, suggesting that current design guidance of 0.25 g may not be conservative. Age and gender were not significant predictors of PRT or deceleration rate, whereas self-identified bicycling confidence was significant in predicting both variables. Speed was also found to be a significant predictor of PRT. This study is the first to measure on-road bicyclist perception-reaction time and braking in unalerted conditions, and provides valuable evidence to inform design guidance for bicycle facilities.