I think it depends on the girl. Some girls are very flirty and will look at guy easily. Others, who might be more shy could very well look away or down. I am much older than you but can tell you that when a cute guy walks by, I have always looked away while still trying to catch a glimpse before they get too close. I wish I could feel confident to look at them! Hope you don't take this the wrong way (since I am a lot older than you), but my guess is that they might be intimidated. You are a very nice looking guy. Just don't assume they don't like you because they don't look. You need to just bring out a good personality and be friendly and once they feel comfortable with you, they will not be afraid to look at you. Hope that helps.
And women are just expected to gawk at you as you pass constantly? Maybe you should try talking to them instead of expecting them to just fawn over you. People complain others don't want them, then do nothing proactive about it.
If an attractive dude walks near me I do make eye contact with him for a few seconds and then look away if he looks back (im very curious, so I always try to look at their eyes)
and of course, it could also happen that the girl pretends she was not looking...hence, it depends of the personality of the girl (:
It doesn't matter if a girl is shy or not, it just does matter if she is interested in the mysterious or pretty looks of the guy.
Starling is right about expecting anything: do not expect that every single girl that walks by you stares at your face like WOW.
Do me a favor and when you make eye contact with another girl that gets your interest and attention, try to talk with her later instead of wondering if she thought that you were a pretty face or the ugliest thing ever XD