I doubt that speed was a factor at all in this unfortunate incident.  It's probably much more likely that the driver did not see the couple in the dark, while turning with headlights shining straight ahead. 

Therefore I hope you are aware that River Road is poorly light, and how important it is for pedestrians and bicyclists make themselves visible, and be conscious of the fact that car headlights do not shine around corners.  Reduced speed can not be assumed as any kind of substitute for such common sense.