What's "backs up" and "surface streets" meaning in this paragraph ?

On a summer afternoon, the drive home
from the University of Chicago to the
north side of the city must be one of the
most beautiful commutes in the world. On
the left on Lake Shore Drive you pass Grant
Park, some of the world’s first skyscrapers,
and the Sears Tower. On the right is the
intense blue of Lake Michigan. But for all the
beauty, the traffic can be hell. So, if you drive
the route every day, you learn the shortcuts.
====================================
You know that if it backs up from the Buck-
ingham Fountain all the way to McCormick
Place, you’re better off taking the surface
streets and getting back onto Lake Shore
Drive a few miles north.
分割线下面的部分请帮我翻译一下，谢谢！backs up 啥意思？surface streets啥意思？

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