The westbound (northbound) I-74 bridge predates the interstate highway system by more than 20 years.
As revealed at a Bettendorf City Council meeting, construction on the new I-74 bridge will begin in 2019 with expected completion around 2023. The first letting on related street projects, the designs of which have been altered during planning, will be in 2014. This document from 2004 (PDF) had a 2015-20 time frame for bridge construction.
Work on plans to replace the I-74 bridge began in 2004. At the time, the estimated cost was $600 million. In December 2011 it was $767 million and may be $1.4 billion by the time it is actually built, according to this item from the city of Bettendorf’s website.
If this timeline holds, that’s 19 years from start of plans to open bridge. It was 24 years and one month between opening of the two spans that currently serve as the I-74 bridge. The older/westbound span will be 85 years old in 2020 and the younger/eastbound span will be 60 in 2019.
My I-74 terminus page is here.