 State and federal agencies are in the process of replacing the Tappan Zee Bridge over New York 's Hudson River . The original Tappan Zee bridge is a cantilever bridge built during 1952 – 55 . The bridge is three miles ( 4 @.@ 8 km ) long and spans the Hudson at its second @-@ widest point . The deteriorating current structure bears an average of 138 @,@ 000 vehicles per day , substantially more traffic than its designed capacity . During its first decade , the bridge carried fewer than 40 @,@ 000 vehicles per day . Part of the justification for replacing the bridge stems from its construction immediately following the Korean War on a low budget of only $ 81 million . Unlike other major bridges in metropolitan New York , the Tappan Zee was designed to last only 50 years . The Federal Highway Administration issued a report in October 2011 designating the Tappan Zee 's replacement to be a dual @-@ span twin bridge . The new bridge is now under construction a few yards to the north of the existing bridge , and will connect to the existing highway approaches of the New York State Thruway ( I @-@ 87 / I @-@ 287 ) on both river banks . Construction began in 2013 , with opening targeted for 2018 . When completed in 2018 , the new Tappan Zee Bridge will be one of the longest cable @-@ stayed spans in the nation . 
