Answer:
The road was expected to be built by us.
Explanation:
First, identify the direct subject of this sentence, which is <u>they</u>. Remember to always change things in the independent clause. Then place the indirect object of the sentence at the beginning, which is <u>the road</u> in this case.
Because you can't exactly write "the road was expected to be built by us by them," completely rule out the word <u>them</u>. Now, switch things around until they make the same meaning (except wordier), and voila - you are done.
Note: most of the time, passive voice is wordy and hard to read, so stick with active voice for other writing.
Hope this helps! :)