It's surely been discussed here before. This movie is immediately identifiable as a noir in the first 2-3 minutes. The sound track and music, the montage, the voice over, the uneasiness or disorientation generated by the editing, which alternates Hollywood views, traffic signals and the uneasy face of Jane Randolph as cab driver. I love it. Lots of noirs have this feeling, like The Amazing Mr. X, The Gangster, Voice in the Wind, and part of it is sonic.
Next one up, for my wife, is Interlude (1968) and its opening has this uneasy quality too. Her favorite lately has been Across 110th Street, which is very different.