By Joe Vazquez

SAN FRANCISCO (CBS SF) — Two critical skateboard-related injuries in Dolores Park led to the weekend installation of speed dots in an effort to curb “hill bombing” which authorities say has become more dangerous in recent weeks.

On Sunday night, A group of bicyclists gathered at Dolores Park for a vigil. Their friend was riding his bike Friday night when, authorities say, he collided with a skateboarder.

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“Super creative, always dancing, super happy. Such a nice guy to be around,” said Sofia Montes about her coworker.

Authorities have not released the name of the victim, but the SFMTA said he suffered life-threatening injuries. A teenage skateboarder was also badly injured in a separate incident at Dolores Park on Friday.

“He was bleeding on the street. He got taken away in an ambulance,” said Corey Crellin, who saw the teenager just after the crash.

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“We’re certainly not anti-skate at the SFMTA [but] we did need to stop what was happening,” said Jeffrey Tumlin, the director of the SFMTA who ordered raised speed dots to be installed this weekend on Dolores and 20th Streets in an effort to slow the traffic down.

For years, young people on skateboards and bicycles have gathered at Dolores Park to take advantage of the steep hills and perform stunts and let off steam. They have also occasionally gotten hurt. And gotten in scrapes with police.

The Dolores Hill Bomb is usually a once-a-year event, but there have been 3 gatherings in the last couple of weeks.

“The vast majority of skaters who bomb Dolores Hill pay very careful attention to other people,” said Tumlin. “What was happening on Dolores was attention-seeking thrill-seekers who were not taking care of other people on the street. And we had more than one severe life-threatening injuries.”

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Some skateboarders told KPIX5 off camera they will find a way to continue to hillbomb. If not at Dolores Park, then somewhere else in the city.