What is the technical definition of a forest, and does London meet the requirements?

I live in central London (anyone who has driven through London will feel my pain here) and have several near-misses each month crossing the road on the way to school. I haven't been hit (fortunately) but have found that every time I have nearly been hit I freeze- even if I'm in the middle of the road.

I don't quite understand why I do that; I didn't stop consciously and it would surely make sense for me to keep walking until I was out of danger.

Could someone please explain this to me?