Customize safe speeds for vehicles are determined from information that is collected from multiple trips and multiple drivers across many road segments. The information collected includes the speed traveled along the road segment, possibly along with additional information, such as (for example) driver, time of day, day of week, weather and road conditions, angle of the sun or other factors. Given information from a new trip, the driver's speed can be compared on each road segment with relevant data from previous trips (from e.g., similar roads, weather conditions, drivers). The comparison yields a score representing the safety of the driver's speed.