In a former life I ran, and ran alot at night, and given a few minutes in the darkness, my eyes were able to adjust to the point where even the light from a quarter moon would be enough to run 5 miles along a unlit track along side a quarry. It was a well used track, used by runners, cyclist, as well as dog walkers and couples. I can say that I've never "run into" anyone. Cyclists make more noise than runner, even runners make a pant pant flap flap noise, loud enought that you can spot and avoid them when you're 20 or 30 feet away. Dog walkers or their waterproof jackets tend to make a noise like a crisp packet, and dogs claws on the ground make a click click noise. If you are paying attention you can see dark on dark movement solely becasue it is moving. However you have to be paying attention... and that is the key.