Answer:
The road was expected to be built by us.
Step-by-step explanation:
First, identify the direct subject of this sentence, which is they. Remember to always change things in the independent clause. Then place the indirect object of the sentence at the beginning, which is the road 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 them. 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! :)