SQL> select  * from road;

    IDROAD ROAD_NAME            ROAD_BEG_KM ROAD_END_KM CORTIME
---------- -------------------- ----------- ----------- --------
         1 Lviv                          10         110 21.08.17
         2 Nadzeya                       10          15 21.08.17
         3 kiev                         100         700 21.08.17
         4 Samara                         0        3000 21.08.17

SQL> select * from bridge;

  IDBRIDGE BRIDGE_NAME              IDROAD    ROAD_KM LENGTH_OF_BRIDGE CORTIME
---------- -------------------- ---------- ---------- ---------------- --------
       100 Sm                            4        200             40,5 21.08.17

SQL> select idroad from road
  2  where (road_end_km-road_beg_km)>10
  3  and not exists
  4  (select * from bridge
  5  where bridge.idroad=road.idroad);

    IDROAD
----------
         3
         1

SQL> declare
  2   procedure   add_month(p_idroad number,p_length_road number,p_road_name varchar2) is
  3   begin
  4     insert into bridge (idbridge,bridge_name,idroad,road_km,length_of_bridge,cortime)
  5     values
  6     ((select nvl(max(idbridge),0)+1 from bridge),'Новий міст'
  7       ,p_idroad,p_length_road/2,length(p_road_name),sysdate);
  8   end;
  9  begin
 10   for r in (select idroad,road_name,(road_end_km-road_beg_km) length_road from road
 11             where (road_end_km-road_beg_km)>10
 12                    and not exists
 13                      (select * from bridge where bridge.idroad=road.idroad)) loop
 14    add_month(r.idroad,r.length_road,r.road_name);
 15   end loop;
 16   --commit;
 17  end;
 18  /

PL/SQL procedure successfully completed.

SQL> select * from bridge;

  IDBRIDGE BRIDGE_NAME              IDROAD    ROAD_KM LENGTH_OF_BRIDGE CORTIME
---------- -------------------- ---------- ---------- ---------------- --------
       100 Sm                            4        200             40,5 21.08.17
       101 Новий міст                    3        300                4 21.08.17
       102 Новий міст                    1         50                4 21.08.17

SQL> rollback;

Rollback complete.

      select  (road_end_km - road_beg_km) / 2,
              length(road_name)
        into  km,
              length_bridge
        from  road
        where idroad = id_road;