The first weekday commute after a train derailed and smashed into a bridge connecting thousands of workers to Swan Island included lengthy delays on the main roads leading to the job hub.

Westbound motorists on North Going Street sat in stop-and-go traffic from the Interstate 5 offramp to the employment center about a mile to the west. Traffic on North Greeley Avenue backed up, too, as cars and trucks traveling to Swan Island backed up by the dozens.

City transportation officials warned that traffic snarls may be the new normal for the time being, perhaps even for weeks or months, as engineers worked to examine how extensive the damage is and what to do next. People who need to get to and from the island should plan for potentially significant delays.

Dylan Rivera, a Portland Bureau of Transportation spokesman, said crews learned Sunday that the damage from Saturday’s train derailment was worse than initially thought.

A northbound train Saturday morning derailed and slammed into concrete support beams on the busy North Portland bridge, which Rivera said is actually three connected structures. On Sunday, engineers observed that the locomotive struck and damaged two concrete beams and potentially the bridge deck itself. On Saturday, officials had believed one beam was damaged.

Rivera said the support beams rest on concrete footings, which sit on top of pilings driven deep into the ground to keep the bridge stable. It’s possible those structures were also damaged.

“We’re going to dig around the column to see if the footing or pilings are also damaged,” Rivera said Monday. “That will tell us how big a job we have to make it safe.”

Structural engineers have so far deemed only two of the six lanes on the North Going Street bridge safe for traffic.

Those two lanes are on the north side of the bridge.

Amy Lewin, a spokeswoman for the Portland Business Alliance, said the crash’s impact “is simply immeasurable at this time.”

“We hope city engineers are able to find a way to fix it fast. This is an important route not only for those who work on Swan Island but the many businesses that support our region, moving goods and services throughout,” she said in an email.

Vigor, a ship building and manufacturing company with more than 900 employees and subcontractors on the island, said it had to adjust shifts on Monday to try and stagger commute times. “As needed, we’ll adjust going forward in a way that minimizes the impact on our operations as well as congestion issues,” said Jill Mackie, senior vice president for public affairs. “We have reached out to establish direct two-way communication with city transportation officials so we can have the information we need in a timely way to maintain ongoing operations.”

The bridge crosses over a Union Pacific rail yard and serves as the sole public route for thousands of workers and delivery drivers coming and going from Swan Island, home to several warehouses and assembly centers. The traffic delays could be particularly painful for shipping firms such as FedEx and United Parcel Service, which both operate large hubs on the island.

The crash occurred at 9:19 a.m. Saturday after a Union Pacific train left the tracks and struck the bridge.

Tim McMahan, a Union Pacific spokesman, said the two locomotives and three tank cars derailed in the incident. Those derailed vehicles “collided and cracked a support beam” he said in an email. The tankers contained liquified petroleum gas. The company is investigating what caused the crash. No cargo spilled from the train, the company said, and no one was injured.

Rivera said the city set up a special website and email notification for people who want to have updates about the status of the bridge repairs and closure. As of Monday morning, 90 people had signed up since Sunday, he said.

-- Molly Young and Andrew Theen

myoung@oregonian.com + atheen@oregonian.com