The provisions of this chapter are not intended to prevent the installation of any material, or to prohibit any design or method of construction not specifically prescribed by this chapter, provided that any such alternative has been preapproved by the City Engineer or his/her designee. An alternative material, design or method of construction may be approved, where the City Engineer determines that the proposed design is satisfactory and complies with the intent of this chapter, and that the material, method or work is offered for the purpose intended, and is at least the equivalent of that prescribed in this chapter in terms of quality, effectiveness, durability and safety.