San Francisco crossing guard, 82, holds down "Granna's Corner" for nearly two decades

The whistle comes first. Then the booming voice.

"Ah-ah — are you going to come back?" Marian Greenfield calls out to a pedestrian easing into the crosswalk at Oakdale Avenue and Keith Street. "That's against the rules and regulations."

Greenfield, 82, has worked this corner in San Francisco's Bayview neighborhood for so long that it no longer goes by the street names. Outside George Washington Carver Elementary School, everyone calls it "Granna's Corner."

This is her 19th school year as a crossing guard with the San Francisco Municipal Transportation Agency, one of 175 guards stationed across the city. In a bright yellow vest, she is part traffic cop, part grandmother to every child who crosses in front of her outside George Washington Carver Elementary.

"Everybody love her," one mom at the corner said. "Everybody love her."

She is sweet. She is also stern — and she makes no apology for it.

"Anyone can get hurt at any time, so you have to be aware," Greenfield said, after a morning that included more than one close call.

Her job description ends at the curb. What she does for the students does not.

Part of the paycheck Greenfield earns goes right back to the children she guards. She also keeps warm socks and clothes in her car to hand out to students who need them.

"I have sent kids to school, and they come back and say, 'Granna, I really appreciate what you've done,'" she said. "Every little bit helps."

The morning rush is only half the shift. When the last student has made it through the intersection, Greenfield heads out.

"Breakfast, and then go to Bible study, then come back up here," she says, before returning for afternoon pickup.

At 82, Greenfield thinks she still has a couple more years in her monitoring this intersection.

"It's good to keep moving and help someone," she said. "I love my corner. Keith and Oakdale. Granna's corner."

And don't you forget it.