The proposed pedestrian and bicycle bridge over I-5 at Northgate – linking the North Seattle College on the west with the bus and (future) light rail transit center on the east – has to be pretty high for vehicles on the freeway to pass underneath. That height (about 40 feet above 1st Avenue NE) makes for a looong approach ramp, over 1500 feet, most of it up in the air.
Traditionally these bridge types are steel, and that is what the design codes reference, but SDOT’s team is considering the possibility of using carbon fiber – the stuff that Boeing uses in the 787. Carbon fiber is ten times as strong as steel at less than a quarter of the weight which enables longer spans, smaller foundations, faster construction and less traffic disruption. Andy Bridge, Director of Research and Development for Janicki Industries, says other advantages include reduced visual impacts due to a thinner support structure, easily formed organic shapes, and lower maintenance costs.
The SDOT Northgate Pedestrian and Bicycle Bridge team will be considering many factors – principally safety – in making design decisions, but is excited about the potential of new materials and methods. This is just one way in which SDOT is seeking to take advantage of innovations in design to reduce costs and provide great service.