The cause of death was blunt force injuries to the head and trunk, the spokeswoman said. Ms. Johnson, who was wearing a helmet and riding with friends, hit her head in the fall, Menlo Park police said.
The incident occurred on Sand Hill Road west of Branner Drive in Menlo Park while the group of cyclists was heading east.
About a mile west of that spot on Sand Hill Road and on Alpine Road, lower speed limits will be going into effect in January following a recent decision by the San Mateo County Board of Supervisors.
New speed limits
Ms. Johnson's accident is one of five major accidents involving bicyclists on the Sand Hill/Portola/Alpine Road cycling loop over the past 12 months.
The current 55 mph limit on Sand Hill between Whiskey Hill Road and Interstate 280 will drop to 50 mph in January, in part because of the high volume of cyclists in that area, said Lisa Ekers, the county's road operations manager.
The county supervisors on Dec. 4 also approved a 40 mph limit, down from 45 mph, on Alpine Road between La Cuesta Drive in Ladera and Junipero Serra Boulevard in Menlo Park.
In December 2006, Menlo Park resident and bicycle racer MaryAnn Levenson, 48, suffered severe injuries to her head, neck, spine, ribs, airway, pelvis, arms, legs and feet when an allegedly drunken driver in a pickup truck struck her and dragged her about 35 feet.
In May, Portola Valley resident and former Altera Corp. chief executive Rodney Smith, 67, died at the side of the road after his bicycle was struck by a car near the crest of the hill between Interstate 280 and Whiskey Hill Road.
A few days later in May, cyclist Debra Weil, 51, of Menlo Park survived a severe collision with a car at the intersection of Sand Hill and Portola roads, but with major injuries to her face and arms.
On June 30 on Alpine Road near Golden Oak Drive, a 50-year-old cyclist from Pacifica suffered a fractured skull and facial trauma after colliding with the passenger-side rear view mirror of a Cadillac driven by a 91-year-old resident of Portola Valley. The cyclist had moved out into the traffic lane in a passing maneuver, a San Mateo County deputy sheriff said.