关于助动词省略问题·

逆水潜龙

Dirt roads may evoke the bucolic simplicity of another century, but financially strained townships point out that dirt roads cost twice as much as maintaining paved roads.

B.dirt roads cost twice as much to maintain as paved roads do

我想请教B中 paved roads do ，do是代替costs，抑或是do （costs），把costs省略了？
还有paved roads do 中do能否省略？不是说没宾语.dirt roads cost 不产生歧义就可省吗？如I eat as fast as you （eat）。。。