With single yellow lines people can load and unload and I get the feeling that some people take advantage of that. A parking warden would need to see you parked for at least 5 minutes before issuing a ticket. On Sundays people can currently legally park on most of Dartmouth Road, which completely prevents buses passing each other. At least on other days the illegal parking on single yellows is limited to a small number of cars, so buses can eventually find a way to squeeze past each other.

People rarely park on double yellow lines (or red lines) as they know they are much more likely to get fines and other road users are far less tolerant of such behaviour. In addition when new parking restrictions are introduced parking enforcement is tightened up to ensure people park legally.

I completely agree with your idea of a footbridge across the railway. Sadly this would cost about £3m, so I don't think it is very likely (and nor did the head of planning for Lewisham when I spoke to him about it a year ago). But there is a car park behind Sainsburys, closer to the shops than any of the car parks in Bromley town centre are to the shops, and free for two hours.

Sadly motorists (including me) are lazy - once you are in a car you want to park as close to the shop as possible, even if this means spending 2 minutes circling round the block looking for a space, rather than using the car park which is three minutes away from the destination.