4. In carrying out the works authorised by article 3 (power to construct works) CMAL may deviate laterally from the lines or situations as shown on the deposited plans, sections and elevations to any extent not exceeding the limits of deviation and may deviate vertically from the levels of the works as shown on the deposited plans, sections and elevations to any extent not exceeding 3 metres upwards and to such extent downwards as may be found necessary or convenient.