A visualisation of the northern tunnel portal to be build for the Warkworth to Te Hana expressway. (Image: NZTA/Supplied)A $3.6 billion public-private partnership contract to build the Warkworth to Te Hana expressway – New Zealand’s most expensive roading project – has been struck between the transport agency and Northway consortium.Financial close of negotiations between NZ Transport Agency (NZTA) and the consortium led by Spanish infrastructure builder Acciona took place on Thursday afternoon.The Northway consortium includes Acciona Concesiones SL, Acciona Construction NZ, and Aberdeen Investments. Downer and AECOM have been subcontracted by N...