Sticks out your wand arm at the kerb. The knight bus will appear
In Harry Potter and the Prisoner of Azkaban the Knight Bus has to squeeze between two oncoming double-decker buses on Lambeth Bridge, which is the bridge upstream from Westminster Bridge.
A purple, triple-decker bus, the knight bus has seats during the day and beds at night. It takes stranded witches and wizards in urgent need of transportation where they need to go.
It is not particularly comfortable, and I would advise against ordering hot drinks, because the bus’s habit of leaping from one destination to another at a moment’s notice can result in a lot of spillage.