Below are three superb clips off Youtube, from transport enthusiast and local historian Duncan Holden. Please take 5 minutes (they're only short clips) and have a look at them. I particularly like the Salford Bridge one. It was as busy back then as it is now, perhaps busier traffic wise.
Follow the links (side panel) and check out Duncan's website. The best collection of old Blackburn trams and buses you'll ever see.
Used here with kind permission and courtesy of Duncan Holden.