The department may be appointed by said authority as its agent for the purpose of constructing improvements and extensions to the Jacksonville Expressway System and for the completion thereof. In such event, the authority shall provide the department with complete copies of all documents, agreements, resolutions, contracts and instruments relating thereto and shall request the department to do such construction work including the planning, surveying and actual construction of the completion, extensions, and improvements to the Jacksonville Expressway System and shall transfer to the credit of an account of the department in the treasury of the state the necessary funds therefor and the department shall thereupon be authorized, empowered and directed to proceed with such construction and to use the said funds for such purpose in the same manner that it is now authorized to use the funds otherwise provided by law for its use in construction of roads and bridges.