Power to adopt, construct or alter any sub-way, bridge, etc.-

The Commissioner when authorised by the corporation in this behalf, may agree with any person,-

1. (a) to adopt, and maintain any existing or projected sub-way, bridge, aqueduct or arch, and the approaches thereto and may accordingly adopt and maintain such sub-way, bridges, aqueduct or arch and approaches as parts of public streets, or as property vesting in the corporation; or
2. (b) for the construction or alterations of any such sub-way, bridge acqueduct or arch or for the purchase or acquisition of any adjoining land required for the foundation and support thereof or for the approaches thereto, either entirely at the expense of such person or partly at the expense of such person and partly at the expense of the corporation.