A specification for street lighting requires an earth electrode at the beginning of the circuit and at the end of the circuit both having an Ra of not more than 20 ohms (Is this a common spec?.) The single phase circuit will be lifted off a DNO PME supply and supply 16 columns of galvanized steel construction. My view would be that the columns will offer a relatively good connection with earth when considered globally. I intend to measure the arrangement using the two clamp method which we use for lightning system earthing. I would be surprised if it didn't offer something below 10 ohms.