] Especially the one on the left side at the end of the picture made me wonder how the ladies safely crossed the streets when adorned with such headgear!

You may not see the lady's eyes, but she can see more than you think. Her range of vision above is somewhat limited, but she can see at the sides simply by turning her head. (Trust me, I know.) Furthermore, crossing the "street" was not the issue in the 18th century that it is today. Certainly, one could be hit by a carriage, but chances are the lady who wore this hat was driven wherever she had to go.