Whenever the legislature specifically authorizes, as a single project, the construction of an additional toll bridge, including approaches, and the reconstruction of an existing adjacent bridge, including approaches, and the imposition of tolls on both bridges, the department is authorized to enter into appropriate agreements whereunder the existing bridge or its approaches will be reconstructed and improved and an additional bridge, including approaches and connecting highways will be constructed as a part of the same project to be located adjacent to or within two miles of the existing bridge and will be financed through the issuance of revenue bonds of the same series. The department has the right to impose tolls for traffic over the existing bridge as well as the additional bridge for the purpose of paying the cost of operation and maintenance of the bridge or bridges and the interest on and creating a sinking fund for retirement of revenue bonds issued for account of such project, all in the manner permitted and provided by this chapter.