I would recommend that you find the plat for your subdivision as it will probably have an answer for you. Streets are usually dedicated for public use solely by the plat. There will be a dedication to public use statement, and there will be a bunch of approval signatures from all of the public entities involved. It is highly unlikely that your subdivision came into existence without these signature approvals. If the city accepted the street dedication, the streets are public whether the city improved them or not.

