Where obstruction lighting is installed on obstructions which are located along or near railroad rights of way and thereby constitutes a potential hazard to the safe operation of railway trains, extreme care should be taken to prevent any possibility of these obstructions lights being mistaken by locomotive engineers for railway signal lights. Shielding of the obstruction lights from the view of the locomotive engineers, if practicable, should be considered; the fixed lights on the obstruction may be made to flash; or the lights at the lower levels of the obstruction may be extinguished if their extinguishment does not materially increase the hazard to air navigation caused by the presence of the obstruction.