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The Portland Bureau of Transportation is moving forward with plans for a 470-foot-long bridge spanning Interstate 84 to aid pedestrians and bicyclists.

A preliminary design for Sullivan’s Crossing calls for a tied-arch bridge that would be 24 feet wide, with space only for bicyclists and pedestrians. Motor vehicles would not be allowed on the bridge in normal circumstances.

The bridge is intended to fulfill a purpose that adjacent streets do not: nonmotorized transportation, according to PBOT project manager Dan Layden. Two nearby thoroughfares, Grand Avenue and Martin Luther King Jr. Boulevard, don’t have bike lanes at all, and present challenges for pedestrians.

鈥淭hey don’t work at all for bikes,鈥� Layden said. 鈥淚t’s a pretty uncomfortable environment to walk in. As (the Lloyd District) develops, and the Central Eastside develops, there’s more demand for bicycle and pedestrian connections.鈥�

Plans call for the bridge to connect Northeast Seventh Avenue and Lloyd Street on the north to Seventh and Flanders Street on the south.

The bridge’s design is being driven in part by the need for substantial clear heights over Interstate 84 and Union Pacific railroad tracks. PBOT is also prohibited from placing any bridge supports in Oregon Department of Transportation’s right-of-way along I-84, which means building nothing on the shoulder or the median of the interstate, or on the south hillside.

鈥淭he site constraints 鈥� the geography and the right-of-way situation 鈥� were impactful in the design,鈥� said Stephen Whittington, a KPFF structural engineer.

The $13 million project is being funded by system development charges and a $2 million contribution from Prosper Portland. Construction is expected to begin in July 2019, with completion in 2020.

Sullivan’s Crossing will be built to contemporary seismic standards and is expected to be able to survive a major earthquake. The bridge is also designed to be used by emergency vehicles if necessary.

Unlike Tilikum Crossing 鈥� a 1,720-foot-long span over the Willamette River, Sullivan’s Crossing will not accommodate light rail and buses. The design team worked to create a design that was distinct from Tilikum Crossing.

鈥淲e wanted to be careful we didn’t replicate that or create a mini version of it,鈥� Whittington said.

Members of the Portland Design Commission praised the bridge design at a briefing last week.

鈥淚t’s really quite beautiful,鈥� Commissioner Tad Savinar said.

It’s a 鈥渘eat and elegant asymmetrical design,鈥� Commission Chairwoman Julie Livingston said. But the north end 鈥渁esthetically looks a little underdone,鈥� she added. 鈥淚t seems a little too slender, and yet not quite slender enough. It’s a visual balance issue with the bridge.鈥�

In addition to KPFF, Architectural Applications and ZGF Architects are on the design team. John Breshears, president of Architectural Applications, said the bridge deck could be lit with recessed fixtures, with a possible tree-like lighting structure installed on the south end.

ZGF is on board to help integrate the bridge into the surrounding urban infrastructure. Sullivan’s Crossing is considered part of the Green Loop 鈥� a 鈥渓inear park鈥� that would link downtown and the Central Eastside with bicyclist- and pedestrian-friendly connections.

鈥淭hese landings all become an episode for the Green Loop,鈥� said Trent Thelen, an associate partner at ZGF.

The project team is also deciding between white paint and a weathered steel look for the bridge. Design commissioners said they prefer white paint.

An open house to learn more about the project will take place Monday, from 4-6 p.m., at Metro Regional Center, at 600 N.E. Grand Ave.