The Luís I Bridge (Ponte Luís I) is a metal arch bridge that spans the Douro River between the cities of Porto and Vila Nova de Gaia in Portugal. At the time of construction its span of 172 m was the longest of its type in the world.
Originally built to take road traffic on both decks, at various times it saw trams on the upper and trolleybuses on the lower. The top deck is now occupied by Line D of the Metro do Porto and a pedestrian walkway.