Elliott Bay Trail--DNA Bridge
Elliott Bay Trail
The helical bridge looks like a DNA molecule for a reason:  it was designed that way for Amgen, the world's largest independent biotech firm.
It provides a way for pedestrian and cycling employees to cross the highway and tracks to reach Amgen.  The bridge is open to the public.
Since stairs lead up to the bridge deck, runnels for guiding a wheel up the incline are provided.
Runnels probably work better for two wheels than three.
The elevators are an option to the runnels.
Carrying is another way to navigate the stairs.