On 23/04/2010 03:31, Thumper wrote:
1. Is there a short bridge that one could cross either at the end of
Portobello Road (or perhaps on an adjacent street?).

There is a blue footbridge called the Halfpenny Bridge over the Grand
Union Canal opposite Second Avenue. I thought it was a new bridge (last
10 years) but there is a road called Tollbridge Close near the southern
end, which suggests there was an older bridge nearby.

2. Also, is there a plaza next to a place where a train drives over an
overpass?

This sounds like a reference to the demolished footbridge over Shepherds
Bush Green, which looked like an InterCity 125. The W12 shopping centre
was (is) at the southern end.