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Multnomah County commissioners on Thursday OK’d studies of four possibilities for the future of Burnside Bridge.

Two of the options would involve building new bridges with a lift in the middle of the span. Another option would involve retrofitting the existing 93-year-old bridge. The final option would be to do nothing 鈥� the 鈥渘o build鈥� scenario.

The construction options range in cost from an estimated $550 million for a retrofit to $850 million for a new bridge.

Commissioners unanimously approved moving forward on an environmental impact study of the four options. They also agreed on a hefty raise to vehicle registration fees to help pay for it.

Retrofitting the Burnside Bridge or building a new one is necessary to prevent a catastrophic collapse during an earthquake, according to county officials. A sizable quake could strike Portland at any time, seismologists say, and plunge the bridge into the Willamette River. Scientists estimate there’s a 37 percent chance in the next 50 years of such an earthquake, said Chris Voss, director of the county’s Office of Emergency Management.

A timeline prepared for the Board of Commissioners would have them make a decision on the bridge’s future, known as a preferred alternative, in June 2020.

One scenario the county has jettisoned is construction of a tall, fixed-span bridge. After consulting with the Coast Guard, engineers estimated a fixed span would have to be approximately 140 feet above the river. Because tall bridges also have to be long so the grade isn’t too steep for transportation, engineers estimated the fixed span would be so long that it would touch down near 10th Avenue on each side of the river, county spokesman Mike Pullen said.

A fixed span would be far more expensive and cut off existing businesses from the bridge, Pullen said.

鈥淵ou also start to change the whole street system,鈥� he said.

Commissioners agreed to reject the idea by approving the remaining four alternatives.

Pullen said it’s too early to tell which bridge option the commissioners prefer.

鈥淲e haven’t even really done the deep level of study yet,鈥� he said.

Portland is no stranger to lift bridges: The Broadway, Steel, Morrison and Hawthorne bridges have movable spans, as does the current Burnside Bridge.

The downside to lift bridges is inconvenience; traffic is halted when the bridge is lifted. Lift bridges also must be built to a stouter standard to withstand an earthquake if one strikes while the bridge is lifted, Pullen said.

A new Burnside Bridge would be about 20 feet wider in the middle without the existing bridge’s bell shape. It also would likely have more robust infrastructure for bicyclists and pedestrians, including a possible crash barrier.

County officials are also discussing with their city of Portland counterparts the feasibility of a westbound-only bus lane.

The county recently reconfigured the existing bridge surface to provide a bus-only lane and added plastic wands to separate bike lanes from motorized traffic.

Advocates for bicyclists and pedestrians are eager to push for expanded infrastructure on a new Burnside Bridge.

鈥淭he changes that we’ve seen for the Burnside Bridge as it exists are a step in the right direction,鈥� said Jillian Detweiler, executive director of The Street Trust, a Portland nonprofit group that advocates for bicycling, walking and public transit. 鈥淏ut if they’re building a new bridge, there should really be 21st-century, top-of-the-line biking and walking infrastructure. And it’ll be nice if they’re still around after an earthquake.鈥�

One of the bridge options would involve building a Y-shaped couplet connecting to Couch Street on the east side.

Tradespeople testified in favor of a new bridge during Thursday’s hearing. Desi Wright, a member of the Northwest Carpenters Union, said she was an apprentice during the Sellwood Bridge project and wants others to have a similar experience.

鈥淭his project would create opportunities for people entering the trades,鈥� she said.

The Portland office of HDR, an Omaha, Nebraska-based engineering company, is engaged in the bridge planning effort. HDR evaluated the bridge’s seismic vulnerabilities and is helping design alternatives and reach out to the public.

Commissioners also voted unanimously to nearly triple vehicle registration fees, from $19 to $56, beginning Jan. 1, 2021. Money generated will help advance the project into the construction phase, officials said. The money can also be used to leverage up to $270 million in bond funding, and serves as a prerequisite to obtaining funding from federal, state and local government agencies.

鈥淏uilding infrastructure is hard and it takes a lot of hard work,鈥� Chairwoman Deborah Kafoury said. 鈥淏ut we’ve shown we can do projects that are hard.鈥�

Downtown Portland needs to have a bridge that will survive a major earthquake, Kafoury added.

鈥淲e are not prepared for an earthquake today,鈥� she said.