There are basic legal requirements that need to be adhered before driving, the ability to read a number plate 20.5 metres (67ft) is the legal minimum, but observation depends on much better sight than this.
Observation means using sight, hearing and even smell to gain as much information as possible about surrounding conditions.
Very simply, if you do not know something is there, you can not act upon it. Effective observation gives you extra time to think and act, and so gives you more control over your driving.
Effective observation is a foundation for safe driving and you should therefore never rely upon a quick glance as you may have looked but not really seen what is there.
Glance at the picture quickly, what do you see?
Developing your observation skills
Use your eyes to build a picture of what is happening all around you, as far as you can see, in every direction. The best way to build this picture is to use your eyes in a scanning motion which sweeps the whole environment.
Scan the environment repeatedly for risk areas or hazards, as this will help to reduce your risk of having to brake sharply or having to do a controlled stop.
Check and re-check the distance, the middle ground, the foreground, the sides and rear in a continuous process.
Avoid staring or concentrating on one area in particular despite noticing what you might consider to be a likely problem as this stops you placing them in an order of importance.
How many passes does the team in white make? Test your awareness and Do the Test!
Peripheral vision is the area of eyesight surrounding the central area of sharply defined vision. Although this means what is seen is not as clear, the receptors in this area registers the movement of road users and acts as a cue for the central vision.
Zones of vision
Your zone of vision is what you can see as you look forward and to the side from your vehicle. As you approaching a junction, your zone of vision onto the other road usually improves. You may need to get very close before you can see far enough into the road to know whether it's safe to proceed.
It may be difficult to see some road users, especially when emerging at a junction. Here you will need to pay particular attention to pedestrians who frequently cross at junctions, cyclists who are often obscured behind roof pillars or trees and motor cyclists that may be moving much faster.
If another road user is not in your zone of vision, you're not usually in theirs.
Speed affects observation
The faster you go the further ahead you need to look. Consider, when you driving at 70mph, you will travel 105 feet per second. As your speed increases you need to consciously look beyond where your eyes naturally come to rest.
Your ability to take in foreground detail at these speeds decreases and increases as you slow down. In areas of high traffic density such as town centres, you will have to slow down to be able to take on board all the relevant information.