Autonomous shuttles are becoming a widely used form of public transportation. While autonomous shuttles have advantages to improve safety, potential riders have expressed concerns about falls and injuries sustained during braking events. In the current study we investigated the effects of multiple warning design parameters, including the modality and the temporal aspects of the warning stimulus, on balance maintenance during a simulated hard braking event. Two warning stimuli were used — an auditory stimulus and a visual stimulus. We investigated the effect of the timing of the warning in an attempt to determine how differences in warning time affect preparation for a simulated hard braking event and subsequent maintenance of balance throughout the event. The warning stimuli were presented 200–750 ms prior to the simulated hard braking. We found that participants had more time to prepare for the simulated braking event when presented with the auditory stimulus versus the visual stimulus. We also found that a minimum of a 600 ms warning was required to produce a significant difference in the amount of time to prepare for the simulated breaking event. The results of this current study suggest that given a future automated shuttle that can detect the surrounding environment and reliably predict conditions, then there is a benefit of presenting preemptive warnings for the purpose of maintaining balance and avoiding falls.