Good morning, Sev.
I'm not sure whether you had one dream or two. The complete separation of emotions suggest the latter, but the fact that your roommate was a constant presence says it was only one. Perhaps this will become clear to you as we proceed.
You describe the highway as "lonely." A lonely road is fairly straightforward - you feel as if you are alone in your journey through life. In this case, you have a constant companion. I'm going to go out on a limb and guess that your roommate represents herself, although that is not always the case - she could be a part of your own personality that your roommate reminds you of.
It's snowing hard, which of course is going to limit driving visibility. So not only are you travelling a road that no one else does (so you can't follow anyone else), but you also cannot see what the future will bring.
The man with a gun is a threat, something that frightens you. He doesn't have anyone's face in particular, so you are not clear on the details of the threat. You see him first while your roommate does not, so it's not even an overly obvious threat until you point it out to her. You go back - retrace your steps, relive a part of your lives - to prove that the threat is real. Both times, however, he does not do you any actual harm - he doesn't shoot. So perhaps you are overreacting to a situation in your life which you see as dangerous?
Your roommate is the one driving. This is the main reason that I think she represents herself rather than a fragment of yourself, because when someone else drives your dream car and you are a passenger, this usually means that you do not feel as if you are in control of the relationship - the driver is. Before she turns the car around, you have to convince her of the problem. You are able to do this, but she is definitely the one making the decisions.
Most buildings represent the dreamer's innermost self, because buildings are "where we live." In this case, it's like a hotel, which is usually a temporary home. This may indicate a temporary nature to the relationship (again, with your roommate.) The one child who is being "bad," however, is definitely a rebellious part of yourself. You may feel as if you are reacting inappropriately (maybe as with the gunman?) and are trying to tell yourself to behave and play nice - to stop causing trouble.
Your roommate enter an elevator and go up. This could be a comment on the nature of the relationship (the place you live with her). The upper part of the building is closer to the head (intellect or soul), the middle the heart (emotions) and the lower is the body (instinct or physical). As you are going up, you are letting your higher self rule the relationship, while ignoring the unruly child - an instinct which protests for some reason. I don't get a sense of whether this is the right thing to do, only that this is what you feel you are doing.
I can't comment further without knowing more about what's going on in your waking life, but you may be able to make some connections from all this.