The bridge was designed and built by the Oregon Department of Transportation at a cost of $14 million. The lower southbound deck was opened on October 4, 1966, and the upper northbound deck on October 18, 1966. The main span of the bridge is 440 ft (130 m) long and the two side spans are 301 ft (92 m) each. The vertical clearance of the lower deck is 130 feet (40 m) and the upper deck is 20 feet (6.1 m) above the lower. The bridge is named after Philip Marquam, a state legislator and Multnomah County judge, who owned much of Marquam Hill where Oregon Health & Science University and the Veterans Affairs Medical Center now stand. At the eastern end of the bridge, on the lower deck, is a ramp stub which was intended to connect to the cancelled Mount Hood Freeway. As it has great importance, the Marquam was the first Portland bridge to undergo a seismic retrofit in 1995.
The Marquam Bridge over the Willamette River, viewed from the southwest, atop Marquam Hill
It was built with economy in mind and the public reacted unfavorably to the structure's aesthetics, including a formal protest from the Portland Arts Commission. (In particular, it blocked the view of downtown from the Union Avenue Viaduct.) This led to public input in the design of the Fremont Bridge. During Mayor Vera Katz's State of the City address in 2001, she said, "It’s like having the Berlin Wall dividing east and west, with all the subtle charm of the Daytona 500 smack dab in the middle of our city."
A view of the bridge at dusk
The bridge was designed with three lanes in each direction with shoulders on each deck. Today, it carries four narrow lanes and no shoulders on each deck. Options historically considered have been to reroute I-5 over the existing I-405 alignment, connecting I-84 to I-5 at the Fremont Bridge interchange, following the US 30 alignment, and removing the Marquam permanently. Another option would build a tunnel under the Willamette River approximately following the existing I-5 alignment, and removing the Marquam Bridge permanently. No proposed replacements as of 2008 have kept the existing bridge, or have made it out of committee.