The Ringwood Avenue pedestrian bridge over Highway 101 in Menlo Park is a passage known only to the locals and a few intrepid explorers. Herein I describe this passage for the benefit of science.
This bike / pedestrian crossing is about midway between Willow Road and Marsh Road and is, in my opinion, a much nicer choice over those road crossings. It connects the Belle Haven neighborhood in "East" Menlo Park with the Flood Triangle neighborhood, and is a vital connection to Menlo-Atherton High School for students who live on the (nominally) east side of 101. Here's the view of this bridge from the west side of 101.
For commuters, it's a handy way to cross from the Bay side of 101 to the Caltrain side of the freeway. Typical destinations on the Bay side might be the Sun Microsystems campus or the biotech companies in the industrial parks between Marsh Road and Willow Road in Menlo Park. I've seen people headed to the Menlo Park Techshop use this bridge as well. The entire area bounded by the railroad tracks, Hwy 101 a and Willow Road is mostly residential with lots of four way stops (that are ignored), speed bumps, and other traffic calming measures to prevent cut through traffic.
From the Bay side, I usually ride to the bridge from Willow Road on Hamilton Avenue. Hang a left on Market (jogging around the center divider), then through the traffic circle to the bridge. I sometimes ride down Ivy Drive as well. Google Maps shows a discontinuation on Ivy Dr at the elementary school, but there is pedestrian and bicycle access across there (even if people usually have their cars illegally parked on the access ramps).
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From the Caltrain side of Menlo Park, access is via Ringwood Avenue which runs north (or east or toward the Bay) from Middlefield Road. There's a 5 way stop (that everybody runs, so watch yourself) at Ringwood and Bay Road -- continue straight on Ringwood which becomes a very quiet residential street. Ringwood deadends at the Hwy 101 sound wall -- the pedestrian bridge is on your right.
Hazards are minor: The chicanes at the bridge entry ramps are a pain in the neck. There's often broken glass on the bridge itself. The melanin averse among us sometimes describe Belle Haven as "sketchy," but I've never encountered any problems with my nearly four years of daily, year round bike commuting across this neighborhood. The same goes for several of my cycling colleagues (men and women) who use this bike bridge.
As an FYI, this bridge is supposed to be destroyed and replaced when Caltrans widens 101 by adding a lane between Marsh and Willow. Residents in Triangle Flood repeatedly petition Caltrans and the city of Menlo Park to not replace the bridge during this project; so far Caltrans and Menlo Park have pledged for bridge replacement, but it's important to keep on top of this.