In one of the noisiest, windiest stretches of concrete in San Francisco, a young man with a big red heart in his hands has been dancing joyously twice a week for more than a year - just to make people happy.

It works. And if anyone could use a little cheering up, it's this guy's audience.

He dances for the miserable river of souls grinding their way along Highway 101 during the afternoon commute.

Every Thursday and Friday, from 3 to about 6 p.m., all drivers have to do is gaze up as they pass under the pedestrian bridge that crosses the freeway at 18th Street - and there they will see Ja Vonne Hatfield prancing, spinning and beaming as he taps out spiffy steps and waves his 2-foot-wide foam heart in the air.

The effect on the noisy mess below is electric. Within 10 seconds after he takes up his post, the honking starts. Then the waves and peace signs. And happy shouts dimly filtering up from the roar of the traffic.

Twitter fans and bloggers have wondered who he is and speculated why someone would do such a thing for so long. But it's really simple, Hatfield said.

"It's such a great energy you get from all the people, such a good vibe," he said between dance sets, the bridge's ever-present stiff breeze ruffling his neatly trimmed hair. "This is something so simple, but it can do so much to make someone's day. It makes my day."

'Spreading the love'

The foot traffic also digs the act. The pedestrian bridge is a bit isolated, on the edge of Potrero Hill, and not a lot of people use it. Most have the reaction Kelsey Long, 23, did when she strolled up and stopped short in surprise as her eyes lit on the 22-year-old Hatfield.

In a few seconds she was grinning. "Wow, he's really good! What a treat!" Long exclaimed. She walked over and asked him why he did what he did.

"I'm just spreading the love," Hatfield said, catching his breath.

"Cool," Long said. They slapped a high five. Hatfield went back to his moves.

Holding the heart high above his head, he froze for a moment. Then came a spin. Then a shimmy, a side shuffle and another pose. All the while, the electronic soul beat of the artist Bonobo pounded through his earbuds.

Sometimes he listens to Jay Z, or Drake. A favorite song is "Fly," by Nicki Minaj and Rihanna.

"I came to win, to survive, to prosper, to rise, to fly - to fly," the song goes.

"I like that one a lot," Hatfield said, a little shyly. "It means something."

L.A. inspiration

Hatfield got the idea for his weekly performance last year when he was stuck with a friend in an even more advanced circle of rush-hour hell - Los Angeles.

"I thought, why not help lighten things up back home in San Francisco?" he said. Dancing sprang to mind because he's loved it since learning his first steps as a child in a Baptist church, "and the heart thing came from the idea of wearing your heart on your sleeve."

A few days before Valentine's Day 2013, the dancing began. He hasn't missed a Thursday or Friday since, catching a bus or BART right after the end of his shift as a youth counselor at a group home in the south end of town. He picked the days at the end of the week because he reckons commuters are just a tad more inclined to feel perky with the weekend beckoning.

"It's all just for love, just to make people happy," Hatfield said.

Loves art and people

None of this surprises those who know Hatfield. His father died when Hatfield was young, and he's been on his own since he was 15. That's when his mother died of a heart attack and his brother died of complications from a gang-related shooting.

"Ja Vonne is strong, he loves art and he loves people, so you put those things together and get what he does," said his friend Sabrina Johnson. "He just likes to help people."