They aren't narrow! Slopes don't really add to driving difficulty. Based on what I saw parking on the street generally didn't actually block any lanes - they're mostly designated bays.
I just went to a random location - I promise it's not cherry picked - on streetview:
That's a 2-way road. Quite annoying but pretty common in the UK.
Don't get me wrong - they've absolutely done the right thing by starting in the easiest possible places (Tesla's plan is ridiculous in comparison). I just think it will still be at least another decade before they come to more difficult driving locations.
