Two years ago, a study confirmed what most people in the Tenderloin already knew: The first block of Turk Street, between Taylor and Mason, is one of the most violent and drug-infested stretches of street in San Francisco.

Using San Francisco police statistics, the Tenderloin Housing Clinic survey found appalling numbers. Among them: "Violent crime is 35 times higher than the rest of the city and eight times higher than the Tenderloin at large." Between November 2010 and May 2011, "there were 248 crimes on a block populated by only 438 people."

Nothing seemed to have changed much in the two years since. After the 49ers' playoff loss a few weeks ago, two people were shot on the sidewalk. Just a week ago a man was hit in the head with a bottle at 8 a.m. in front of the Central City SRO Collaborative, which works for tenant safety.

"I can't tell you how many times I've walked right through a drug deal," says Gail Seagraves, a seven-year Tenderloin resident. "You see people shooting up. They don't care."

Until now. Within the past week there's been a minor miracle along the start of Turk.

There are far fewer pedestrians idling about and a dramatic decline in drug dealing. Best of all, there is an improvement in the sense of safety among the residents of the 306 single-room-occupancy units and 80 apartments, which mostly house families with children.

The difference? Parking. Or the lack of it.

Beginning last Friday, both sides of the street in that block of Turk became a no-parking zone. The absence of cars, which used to pull up and linger all day, has changed everything.

"The drug dealers would hide behind the cars," Seagraves said. "It's like a screen. The day (the no-parking debut) happened, we noticed it right away."

Tenderloin police Capt. Jason Cherniss supported the idea wholeheartedly. Since he took over the station last May, he has been an advocate for the effects of environmental design on crime. He took some heat last summer for pushing for the removal of a bus shelter at Eddy and Leavenworth that was a haven for dealers. This, he says, is another good example.

"The hope is the removal of any geographic inconvenience will establish some public safety," he said. "With the (parked) vans and cars, dealers can't be seen."

Supervisor Jane Kim, who represents the district, admits that with the city's chronic shortage of parking, it can be hard to convince people of the benefits of turning a city block into a red zone. But she says there were some compelling arguments about Turk, beginning with the ridiculous crime stats.

"Frankly, a lot of people don't want to park on that street," she said. "And most of the residents don't have cars, so it was mostly used by people driving in from somewhere else."

And often those motorists were drug dealers preying on a vulnerable neighborhood.

"These are people recovering from alcohol and substance abuse," Cherniss said of many of the residents. "And these predators come in from outside and make it easy for them to get these products."

At times, says resident Bryan Johnson, it was more than just making drugs available.

"When I walk through I've had people try to push drugs on me," he said. "I've even had people blow (crack) smoke in my face. I feel like if I had a job interview and a drug test that would show up."

Cynics will say that this is just another example of moving the bad actors around. There's some truth to that. The sketchy individuals have already established spots on nearby streets. But as one Central City SRO organizer says, this block of Turk was so notorious that clearing it out is progress regardless.

All it takes is a reminder of the way it was. Seagraves says that earlier in the week a delivery truck parked briefly to unload items to the corner store. The effect was immediate.

"It was like a beehive," she says. "There were so many people on the street I had to weave between them."

But within minutes the truck was gone, and so were the crowds. It's starting to look like Turk is going to turn the corner - and for once there's not a drug dealer there.