A bicyclist was seriously injured when he collided with the rear of a vehicle in San Francisco’s South of Market neighborhood on Wednesday afternoon, police said today.

The collision was reported at 4:04 p.m. near Fifth and Bryant streets.

The 38-year-old bicyclist was riding behind a vehicle heading north on Fifth Street, and rode into the rear of the car when it stopped, according to police.

He suffered life-threatening head injuries and was taken to San Francisco General Hospital, police said.

No other information about the collision was immediately available.

Cycling advocates have called on San Francisco to increase safety measures in the city’s South of Market neighborhood, where all four of the city’s bicyclist fatalities in 2013 have occurred.

Dan McMenamin, Bay City News