Highway 529 bridge braces are for wind, not support

Mark Kalkoske of Everett writes: Since the collapse of the I-5 bridge into the Skagit River, I’ve been checking out bridges that I drive frequently.

I noticed there is something missing on the northbound Highway 529 bridge over the Snohomish River. Heading north at the third overhead span, one of the lower horizontal girders, in the middle, is not there. This bridge must not be “fracture critical” as was the Skagit River bridge.

I also noticed many “hits” on the other overhead girders, but they are still in place supporting the structure.

Tom Pearce, a spokesman for the state Department of Transportation, responds: This northbound Highway 529 bridge, built in 1927, actually is fracture-critical. However, the girders Mark mentions are wind braces, which are not structurally supportive parts of the bridge. Fracture-critical beams are ones that, if broken, could cause part or all of a bridge to collapse. Wind braces are placed between trusses to keep the trusses parallel and to reduce shaking or vibration in windy conditions.

While wind braces are not fracture-critical parts, they still need to be repaired if they are damaged. On the Highway 529 bridge, the wind braces are about 14 feet, 3 inches over the roadway. To keep them from being hit by trucks, the transportation department installed an over-height detection system on the approach to the bridge several years ago. Despite this, the wind braces still are hit occasionally.

The department is in the process of raising most of the wind braces to 15 feet, 6 inches to reduce this problem. However, near the middle of the bridge there is a bridge house where operators control the draw span. The bridge house is 14 feet, 6 inches above the roadway and it cannot be raised. Because of this, some of the wind braces on the north end of the bridge will be left at the current height to provide a final warning to an over-height vehicle so it doesn’t hit the bridge house.

So why replace any of the wind braces? If a wind brace is hit, it still needs to be repaired. When most of them are higher and won’t get hit, that’s fewer to be repaired, and that will save money.

Dorothy Laymance of Snohomish writes: I drive north on Highway 9, and the left turn light at Cathcart Way always turns red when the northbound traffic going straight turns green. The visibility northbound is almost endless and there is usually no one coming south up the hill because they have been stopped by the light farther north at Lowell-Larimer Road.

Could a blinking yellow arrow possibly replace the red left turn light so drivers could make that turn when it is safe to do so? It would really help traffic flow, especially during the afternoon rush hour.

Tom Pearce of the transportation department responds: We reviewed the intersection of Highway 9 and Cathcart Way to see if Dorothy’s suggestion can be done.

We have criteria to determine if left turns should be protected and require a green arrow, or if they could be permitted on a regular green light when there’s enough room to turn safely. The criteria we use include the number of lanes to be crossed and the speed limit in the area. Because of the speeds on this section of Highway 9 (the speed limit is 55 mph), drivers may not be able to judge gaps in an oncoming stream of traffic, increasing the risk and severity of collisions. As a result, we determined it was best if the left turn movement is protected.

We recognize that many drivers turn left at this intersection, particularly in the evening peak traffic. To accommodate this, we recently made changes to the signals. Now during the evening peak period, we provide a protected left turn for northbound traffic twice per cycle — it turns green at the beginning of the northbound green light cycle and again at the end of that cycle, after southbound turns red.

E-mail us at streetsmarts@heraldnet.com. Please include your city of residence.

Look for updates on our Street Smarts blog at www.heraldnet.com/streetsmarts.

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