Here, opened is the passive participle of open, and it is used to form the passive as you have done here, there is no reason not to. Your sentence is in the past perfect tense, which seems odd, however it may be correct in context.

Yes, things can be opened ; you can use the verb "to open" in the passive form, "to be opened". Your title sentence, though, uses a past perfect tense - "had been opened" - and you would only really use this if you were going on to add something that then happened, like " .. when a large hole appeared under the bridge." Otherwise, a simple past would do : "Last month, the new road was opened to traffic." You could also write, though, "Last month, the new road opened to traffic." https://www.ef.co.uk/english-resources/english-grammar/past-perfect-tense/

The use of the passive past perfect ("had been opened") is incorrect in isolation. The passive simple past ("was opened") is natural for the text that you supplied. However, in context, the passive past perfect may be needed. - The road collapsed last week which is surprising since the road had been opened last month. More information about the past perfect: https://www.ef.com/ca/english-resources/english-grammar/past-perfect-tense/