Mr. Chazelle explained how he and his crew used a freeway right alongside daily commuters, how they got a railway reopened and why he wanted to make real locations look as fake as possible.

Fugue for Traffic Horns

For the opening musical number set in traffic, Mr. Chazelle also wanted to give a sense of how vast the city is. He shot the film in CinemaScope to take it all in. The scene starts with music on the radio and the idea that people stuck in traffic are stars of their own personal musicals. That leads to synchronized singing, dancing and leaping.

The number was shot on a ramp connecting the 105 and 110 freeways. “What I like about it is that you see downtown,” Mr. Chazelle said. “When you go wide and reveal the skyline, it feels kind of ‘Wizard of Oz’ to me, the yellow brick road leading to the Emerald City.” While he joked that his sequence was “as fake as movies get,” he also noted that the road wasn’t blocked off, so in the lower left part of the image, civilian cars are seen driving by as they would on any day. “We’ve established the tension of the movie right away, between really heightened musical fantasia and real, urban modern city.”