Oracle - max date filter issue

  SELECT   DISTINCT A.CARRIER_ID,
                    MAX (A.EFFECTIVE),
                    A.TRLR_TYPE_ID,
                    A.CURRENT_NUM_VEHICLES,
                    L.NAME
    FROM   TL_RESOURCE_TRLR A, CARRIER_EQUIP B,LANE L
   WHERE   A.CARRIER_ID = B.CARRIER_ID(+)
           AND A.TRLR_TYPE_ID = B.TRLR_TYPE_ID(+)
           AND A.LANE_ID = L.ID
           AND B.CARRIER_ID IS NULL -- EXCLUDE ROWS ADDED BECAUSE  OF THE OUTER JOIN
GROUP BY   a.carrier_id, a.trlr_type_id, current_num_vehicles, L.NAME
ORDER BY   A.CARRIER_ID ASC;