520 Trail Grade Separation at NE 40th St
City of Redmond Public Works
190 LF Trail Tunnel, plus transitions
Highways, streets, parking lots
This project contributed significantly to the increased fluidity of pedestrians and cyclists through the intersection at NE 40th Street. The tunnel structure includes retaining walls that will convey the shared use of the SR 520 Regional Trail beneath NE 40th Street.
The tunnel section consists of soldier pile walls with concrete fascia on the tunnel side, and supporting continuous concrete caps on top. Pre-stressed concrete slabs are supported on the cap, and covered with a cast-in-place concrete topping slab.
Tunnel design criteria includes:
Pedestrian Loading in Tunnel: 90 Pounds per Square Foot Pedestrian Live Load
Traffic Loading on NE 40th Street: AASHTO NL-93 Truck Loading
Ramp and Sidewalk Railings: 54-Inch-Tall Minimum
Stairway Railings: 42-Inch-Tall Minimum
Maximum Trail Ramp Gradient: 5% Maximum
Tunnel Service Life: 75-Year Minimum
Tunnel Clear Width: 14 Feet Minimum
Tunnel Minimum Vertical Clearance: 10 Feet
Additional site work includes paved walkways and stairs, requirements of the Americans with Disabilities Act (ADA), utility relocations, lighting and restoration of disturbed surfaces.