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Lake Samish bridge could be narrowed to one lane due to rot

The bridge over North Lake Samish is shown Thursday, Jan. 28, 2016. In their most recent inspection, Whatcom County workers discovered rot in the laminated girders that support the bridge deck. The county is dropping the load rating of the bridge and plans to reduce traffic to one lane.
The bridge over North Lake Samish is shown Thursday, Jan. 28, 2016. In their most recent inspection, Whatcom County workers discovered rot in the laminated girders that support the bridge deck. The county is dropping the load rating of the bridge and plans to reduce traffic to one lane. pdwyer@bhamherald.com

The bridge that crosses the north end of Lake Samish could be narrowed to one lane indefinitely due to wood rot discovered in the support beams.

An inspection of the 250-foot-long bridge in March 2015 found that the tops of most wooden girders that support the deck had areas of rot, according to Whatcom County Public Works.

On top of that, while re-calculating the amount of weight the bridge could handle with the rot, county staff found out that since the last rating was done in 2004, the American Institute of Timber Construction had decided the allowable stress on that type of beam should be reduced by 25 percent.

The new calculations meant that heavy vehicles such as fire engines (38,460 pounds) and 3,000-gallon water tenders (54,220 pounds) that are used to bring water to areas without hydrants might be limited under the stricter weight restrictions.

The county consulted fire officials, who asked to keep the bridge open at least for emergency responses, said Chief Dave Ralston of South Whatcom Fire and Rescue, which responds to emergencies in that area.

“They are going to allow crossings of those emergency vehicles for emergency responses,” Ralston said.

The bridge connects North Lake Samish Drive on the eastern side of the lake with the nexus of West Lake Samish Drive and Roy Road on the western side.

885 Average number of vehicles that cross the Lake Samish bridge every day. School buses cross the bridge six times a day.

Not using the bridge for emergencies on Roy Road would mean crews would need to take the Nulle Road exit off Interstate 5 at the south end of the lake, rather than the exit to North Lake Samish Drive.

“That detour adds about seven minutes in an emergency mode to the call,” Ralston said. “Right now, having that (bridge) open, we’re able to eliminate that.”

Narrowing the bridge to one lane of traffic also would keep it open to much of the regular traffic.

An average of 885 vehicles cross the span a day, and school buses cross the bridge six times a day.

The weight restrictions for heavier vehicles will be posted if and when the bridge is converted to one lane, but for example, a fully loaded 20-foot U-Haul truck would weigh about 15,000 pounds and be well within the allowable limits, according to public works engineering staff.

Bridge options

Public works introduced three bridge options to Whatcom County Council on Tuesday, Jan. 26, with a request that members approve the lane closure — the least expensive option.

At a cost of $15,000, crews could start to narrow the bridge’s traffic lane within a week of council approval, and have the work done within three weeks.

Under that option, stop signs will be placed on either end of the bridge, and traffic guided to a single lane at the center of the bridge, as the edges are the most vulnerable to stress.

The other two options outlined in the staff report would each take an estimated 12 weeks to install. The county could replace the rotting girders at a cost of about $250,000 under one option, or install steel girders to bolster the span’s strength, at a cost of about $450,000 under the other.

County staff asked for the lane closure in part because it would keep the bridge eligible for federal Bridge Replacement Advisory Committee grant money. If the other fixes are made, the county might not be eligible for federal money to aid in repairing or replacing the structure.

The lane closure could be in place for several years until funding for more permanent repairs is obtained, according to staff.

Until council votes on the matter, both lanes of the 1963-built bridge remain open.

Samantha Wohlfeil: 360-715-2274, @SAWohlfeil

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