If you've seen La La Land, you already know the scene we're talking about.
The opening sequence "Another Day of Sun" takes place on the freeways of Los Angeles in some very intense (totally normal) traffic, and includes some pretty fancy camera work.
Director Damien Chazelle even convinced the city of Los Angeles to shut down the freeway ramp connecting to 105 to the 110 for the shoot!
Check out this super cool dress rehearsal, iphone video below:
via Youtube
Source: LAMag.com