Dusty or foggy air, combined with backlight, is a great lighting condition for silhouettes of people and other easy to recognize subjects. This technique creates a mystical, dreamy feeling. In this case, I waited for the moment that the truck's headlights outlined the child on the bike. There is usually a very short timeframe to get this photo right, and since autofocus works off of contrast, I often switch to manual focus in situations like this where the contrast on the subject is very low to non-existent. I was handholding the camera for this shot, so I turned the VC (Vibration Compensation) image stabilizer on, which helps when you are in compromising lighting conditions that require slower shutter speeds.