I don't get it? Why not scream or wave to somebody?

The description says she's kidnapped and locked in the trunk of a cab. But the trailer shows her in the back seat of a conventional cab driving around in broad daylight with the bad guy driving in heavy traffic and no one else in the cab. They never show her in the trunk.

I don't get it, every scene in the trailer she is riding in the back seat like a passenger so why doesn't she scream or wave or something and how can the bad guy stop her, he has no weapon, there is no threat and he's busy driving. Really weird, not believable set up.