SCHEDULE 16  PROTECTIVE PROVISIONS  Article 44  PART 1  FOR THE PROTECTION OF ELECTRICITY, GAS, WATER AND SEWERAGE  UNDERTAKERS  Application  1.  For the protection of the undertakers referred to in this Part of this Schedule the following  provisions have effect unless otherwise agreed in writing between Network Rail and the  undertaker concerned.  2.  The provisions of paragraph 1 of Schedule 15 (provisions relating to statutory undertakers  etc.), in so far as they relate to the removal of apparatus, do not apply in relation to apparatus to  which this Part of this Schedule applies.  3.  This Part of this Schedule does not apply to apparatus in respect of which the relations  between Network Rail and the undertaker are regulated by the provisions of Part 3 of the 1991  Act.  4.  In this Part of this Schedule—  “alternative apparatus” means alternative apparatus adequate to enable the undertaker in  question to fulfil its statutory functions in a manner no less efficient than previously;  “apparatus” means—  and includes a sludge main, disposal main (within the meaning of section 219 of that Act)  or sewer outfall and any manholes, ventilating shafts, pumps or other accessories forming  part of any such sewer, drain or works, and any structure in which apparatus is or is to be  lodged or which gives or will give access to apparatus;  “functions” includes powers and duties;  “in”, in a context referring to apparatus or alternative apparatus in land, includes a reference to  apparatus or alternative apparatus under, over or upon land;  “plans” includes sections, drawings, specifications and method statements; and  “undertaker” means—  (a) in the case of an electricity undertaker, electric lines or electrical plant (as defined in the  Electricity Act 1989( a ), belonging to or maintained by that undertaker;  (b) in the case of a gas undertaker, any mains, pipes or other apparatus belonging to or  maintained by a gas transporter for the purposes of gas supply;  (c) in the case of a water undertaker, mains, pipes or other apparatus belonging to or  maintained by that undertaker for the purposes of water supply; and  (d) in the case of a sewerage undertaker—  (i) any drain or works vested in the undertaker under the Water Industry Act 1991; and  (ii) any sewer which is so vested or is the subject of a notice of intention to adopt given  under section 102(4) of that Act or an agreement to adopt made under section 104 of  that Act,  Interpretation  ( a ) 1989 c. 29.  94