The "S" shape of Lombard Street makes it a perfect spot of fantastic night scenes.
As cars streamed down the street, their head lights appear as light beams when we increase our exposure time.
Use a firm tripod to stable your DSRL and set it to Bulb Mode.
Exposure value: F16, 160 seconds, ISO 250
The technique here is to use a black card--it can be a non-reflective black shirt, cloth or paper card.
You don't want the background to be over-exposed, so we cover the lens with the black card when there is no traffic and remove it when there're cars moving down.
A point to remember is to expose the picture to a maximum of 2 cars. You won't want the light beams to be too messy, so 2 cars would make really smooth and clear beams,