Position yourself with a clear line-of-sight so you can search the traffic environment about seconds ahead.

30 seconds ahead.

Explanation:

Its about 90% of the decisions which are made by someone while driving based on what they see. The vision must be good to make the decision accurately and timely before reacting to the environment.

Line of sight is define as the view which you can see without any obstruction. The best condition of proper line of sight is that someone is needed to see in all direction front, behind, left and right.

To establish the clean line of sight the person should search the traffic environment about 30 seconds ahead.

30 seconds.

Explanation:

The blank will be filled with 30 seconds.

To have a clear line of sight so that you can access the traffic environment you should be 30 second ahead.

To access traffic environment driver should have good vision so that he can gather information accurately and take his decision according to it.

Looking the traffic signal, vehicle around you and flow of the traffic and then acting according to it takes 30 second.