By Emmett Berg

SAN FRANCISCO (Reuters) - A software developer pleaded not guilty on Wednesday to a charge of vehicular manslaughter in the death of an elderly man he is accused of recklessly plowing into while bicycling downhill through a San Francisco intersection.

The case, a rare felony prosecution of a bicycle rider for a fatal accident, comes amid a 71 percent increase in bike traffic in San Francisco in the past five years. It also marks the third instance in which a pedestrian has been killed by a cyclist during the past year in the Bay Area.

Chris Bucchere, 36, is accused of speeding downhill through a red light and into an intersection crowded with pedestrians in the city's Castro District on March 29. He ended up striking Sutchi Hui, 71, who was crossing the street with his wife and died of his injuries four days later.

Evidence against Bucchere, who is free on $150,000 bond, includes several eyewitnesses and a surveillance video that have helped investigators put his estimated speed at up to 35 miles per hour.

A spokeswoman for District Attorney George Gascon's office, Stephanie Ong Stillman, said investigators had evidence Bucchere also ran a number of stop signs on his way downhill to the intersection where the crash occurred.

Authorities also suspect Bucchere was the author of an online blog post about the accident in which the cyclist recalled being "too committed" to stop at the traffic light before going through it.

"I laid it down and just plowed through the crowded crosswalk in the least-populated place I could find," the post said, going on to describe a "river of blood on the asphalt" in the aftermath of the collision.

The San Francisco Chronicle said Bucchere had been trying to set a speed record for a popular bike route through that neighborhood, and an electronic monitoring device on his bike provided investigators with some of their evidence against him.

In a written statement issued to reporters at the courthouse on Wednesday, Bucchere's lawyer, Julie Salamon, said her client "anticipates the day when he may express his deepest condolences to the Hui family for their tragic loss. But for now, while the case is ongoing, he will continue to cooperate with the authorities and to respond responsibly to the charges in court."

Bucchere, who left the courthouse without speaking to reporters following his 10-minute arraignment, is due back in court on July 27, when the judge will set a date for a preliminary hearing.

Stillman said Bucchere was the first bicyclist charged by Gascon with felony vehicular manslaughter, an offense for which prosecutors must show gross negligence and is punishable by up to six years in prison.

In March, cyclist Randolph Ang, 23, pleaded guilty to misdemeanor vehicular manslaughter for running down a 67-year-old woman who died a month later. He was sentenced to three years' probation and 500 hours of community service.

In a more recent accident, a 92-year-old woman was struck and killed by a cyclist in a crosswalk near El Cerrito, east of San Francisco.

(Writing and additional reporting by Steve Gorman; Editing by Cynthia Johnston and Peter Cooney)