Will your headphones help block out traffic noise when I am walking outside?

The Audeara headphones have an active noise cancelling (ANC) feature.

ANC works by picking up low-frequency noise (such as the hum of an aeroplane, air conditioning or background traffic noise) and neutralising it before it reaches the ear. The headphones generate a sound that is the exact opposite (180 degrees inverted) to the incoming noise, essentially cancelling it out. 

Your headphones will help to tone down noise like traffic, but are unlikely to remove it completely.