4. Speed
Looking at the ground beside a moving vehicle helps you judge its speed.
Explanation:
When reading a traffic area you should try to look at the ground around things as you scan. Looking at the ground next to a moving car can help you to adjust the speed or change the speed, and it can tell you whether the other driver is keeping a good lanetion or is about to change direction. Look at things moving in relation to things fixed to make Judgement of speed and distance better.