How come no character ever enquired about the other accident victim?

(SPOILERS!) Whether or not you liked the movie, the surreal fact that no character ever once thought to ask about the condition of the person driving the other car in the pivotal collision (including the woman so haunted over the identity of the other driver), is clear indication that events are not meant to be taken literally (wouldnt neighbors notice the stink of rotting corpses everywhere?), but is instead allegorical on the light and dark sides of the human psyche. The antagonists are not literal demons from another dimension, but rather something more unsettling because they are within us, they ARE us--the primordial 'id', or the 'Devil' that is always subconsciously lurking to destroy life and good. People can murder themselves psychologically, to lose hope and sense of purpose, as exemplified in the opening Poe quote, "henceforward art thou also dead--... to Hope! ... see by this image, which is thine own, how utterly thou hast murdered thyself." Pretty much says it. And despair may be infectious within a society (which could have been explored more, like the subway street-person scene), thus many characters shared the same reversal of character.

So if you are going to criticize why things did not seem to make logical sense, you might as well wonder why you never thought it was strange that the man you were talking to in your dream had the head of a watermelon, until you woke up and began to interpret such 'nonsense.'

The execution is so exacting, you have to concede that the director had a distinct intention. This degree of meticulous personal expression (the director being a renowned photographer, and collaborator with David Lynch who directed another good-&-evil/doppelganger movie- Lost Highway) in a 'horror' film, is not usually about stating the obvious, or satisfying a mass audience. It would not be much of a mystery if everything is explained, although the viewer is shown exactly what is happening (but I thought the shower scene was too overt), yet we are not spoon fed the 'why.' This is where you are meant to have fun exploring the cryptic details, to find meaning for yourself. If you dont want to have to think too much in your movies, then this is not for you.

For example, someone else here criticized the lack of necessity for the scene where the woman is frantic to retrieve a personal photo from the railway, but this may be viewed as her desperation to cling to a 'normal' identity, and last proof of sanity.

Now, what if it had turned out that the original managed to kill the doppelganger?