Subject to the provisions of this Act, the Executive in constructing the authorised works may deviate from the lines thereof shown on the deposited plans or, as the case may be, the substituted plan to any extent within the limits of deviation shown on those plans and may deviate vertically from the levels shown on the deposited sections or, as the case may be, the substituted section to any extent not exceeding 3 metres upwards and to such extent downwards as may be found necessary or convenient and in constructing the tramroads and the tramway they may alter the radius of any curve described on the deposited plans and increase or diminish any inclination or gradient shown thereon.