Designing for a safer bridge
During each phase (planning, design, and pre-construction) of public outreach, we heard that bridge safety is a priority for all bridge users. The sections below outline how safety is incorporated into all aspects of the bridge’s design.
Design
Throughout the design process, we used an approach called Crime Prevention Through Environmental Design (CPTED). This approach is based on the idea that people’s behavior within an urban environment is influenced by the design of that environment.
CPTED strategies include things like providing ample lighting to avoid blind spots, maximizing sight distance and visibility (sometimes called “passive surveillance”), and using materials that promote easy maintenance. This strategy also aims to create spaces that give a sense of ownership of public space and a sense of shared responsibility for personal security.
There are several safety elements on the bridge, including:
- Minimal surface area for vandalism
- Overhead pedestrian lighting
- Emergency call boxes
- Pedestrian guardrails
- Lighting on handrails
- Throw fences
Materials
All bridge materials and connections will go through intensive testing during construction, including the spans across I-5, which will undergo rigorous quality assurance testing during fabrication, assembly, and installation. The trusses of our bridge will be made of steel, a common and proven material and design for hundreds of bridges across the nation.
Life expectancy
Our bridge was required to meet the 75-year design life expectancy criteria consistent with the American Association of State Highway and Transportation Officials (AASHTO) design codes. Not only does our design meet this standard, it’s expected to exceed a lifespan of more than 100 years with routine maintenance during its service life.
Environmental
We selected vegetation and greenery around the bridge with safety in mind. Creating park-like qualities on the trails and spaces near the bridge will provide a comfortable and enjoyable atmosphere and a “sense of place” for all users. Examples of this can be seen on the west side with a wildlife overlook, and on the east side where we’re proposing a “gallery forest,” or screen of tall and narrow trees between the bridge and the freeway, providing relief from views of the freeway and filtering air quality.
Additional environmental features include:
- Planting low-growing shrubs and bushes around the bridge
- Trimming, thinning, or removing existing trees and undergrowth to create open sightlines
- Carefully designed plantings on the west side of the bridge so that pedestrians on the landing will have a clearer view of North Seattle College (NSC), and those on the NSC playing field and in the parking lot will see bridge users approaching
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