Listed on the NRHP on December 17 , 1999 , the Mackinac Trail – Carp River Bridge carries H @-@ 63 , the modern successor to US 2 , over the Carp River north of St. Ignace . The bridge is another spandrel arch structure 60 feet ( 18 m ) in length and built in 1920 . Increasing traffic along Mackinac Trail prompted the MSHD to " widen its deck by five feet [ 1 @.@ 5 m ] and install new guardrails in the 1929 – 1930 biennium " along with the addition of decorative retaining walls .