Someone died here.... That's exactly what I think when I see a cross on the side of a highway. It's a symbol of someone passing, a burial site.
American soldiers are recognized this way on unknown graves. It's a symbol of mourning. I don't think it screams "Christianity!" Ask anybody the question " What do you think of when you see a cross posted on the side of the road?" and their answer will be " Someone lost their life there". They won't say " Oh man, the Christians are forcing their religious beliefs on me"
Of course we have our religious freedoms, other religions should be able to use their choice of a monument to someone's death. But why is it all of a sudden ok to bash the Christians?