A bridge over I-5 connecting Northgate Mall and the planned Northgate light rail station to North Seattle Community College would offer immense benefits to the neighborhood and ridership for the transit line. But it’s not going to be easy.

First, the problem: There is no way to cross I-5 between 92nd St and Northgate Way (effectively 110th St). And since Northgate Way is not at all bike-friendly, the closest I-5 crossing that is not terrifying on a bike is 117th St. That’s a remarkable 25-block barrier without a safe way for people to bike, all in the midst of a rapidly-growing neighborhood. Even without a light rail station, the bridge is needed.

For someone on foot, walking to the new station would require traveling 16–20 extra blocks if there were no bridge. That is enough to discourage a huge number of trips and would essentially leave the station stranded on the edge of a giant parking lot.

But building the bridge will not be easy or cheap. SDOT’s Art Brochet, who is in charge of outreach for the project, presented at Wednesday’s Seattle Bike Advisory Board meeting and explained the biggest cause of bridge challenges: The freeway is elevated above the street level, and highway standards require the bridge to be pretty high above the freeway surface (for oversized vehicles, etc).

Basically, that means the bridge would have to be more than 60 feet above 1st Ave NE. At a five-percent ADA-compliant grade, that’s a couple city blocks worth of ramp just to get to the street. For an idea of how high up the freeway is, here’s a view from 1st Ave via Google Street View: (more…)