Police in Oakland disproportionately stop and search African American pedestrians and motorists under the parameters of “reasonable suspicion” — a vague legal standard that can amount to little more than an officer’s hunch.

From September 2014 to September 2015, more than 34,000 people were stopped by Oakland police, 1,876 for reasonable suspicion. About 70 percent were black, even though just 26.5 percent of Oakland residents are African American, according to a Chronicle analysis.

Reasonable suspicion is the lowest legal threshold officers must clear to conduct a rudimentary search without consent. Unlike traffic or probable cause stops, which require tangible evidence of a violation or crime, reasonable suspicion can be invoked if someone fits a suspect’s physical description, inconsistently answers questions or displays any other signs that they’re engaged in criminal activity.

Because of its broad scope, even legal experts have a hard time defining the term. Critics say it can encourage racial profiling — both conscious and subconscious.

“It’s a horribly defined construct, but it affects the lives of thousands of people in America every day,” said Jack Glaser, associate dean of UC Berkeley’s Goldman School of Public Policy. “The high degree of subjectivity invites implicit stereotypes.”

Ending federal scrutiny

Ensuring that officers stop more criminals and fewer law-abiding civilians is one of the last tasks Oakland police must accomplish before being freed from almost 13 years of federal oversight, which stemmed from endemic misconduct and racial profiling.

While data suggest the department is becoming more precise about whom its officers pull over, it still has work to do. Along with its disproportionate reasonable suspicion stops, more than half the people pulled over for breaking a traffic law over the past year were black, and African Americans accounted for 76 percent of those subjected to a discretionary search — which excludes mandatory searches before a car is towed or an arrest is made.

“Obviously searches are very intrusive, so we want to be sure when we make those decisions we’re making them in a way that’s fair and consistent,” said Assistant Police Chief Paul Figueroa. “We need to continue to be as focused as we can on individuals known to be engaged in criminal activity. We have to be locked in as much as possible.”

Racial profiling in police stops is well documented.

Stanford social psychologist Jennifer Eberhardt has found that police are more likely to conflate African Americans with crime. (Eberhardt is now working with OPD to analyze stop data for instances of racial profiling.) The phenomenon may explain why, during the peak of New York City’s controversial stop-and-frisk policy, the vast majority of civilians subjected to pat-downs were either black or Latino, even though the arrest rates were higher for whites.

The potential of bias creeping into police stops fuels distrust in parts of Oakland. Whether real or perceived, many believe being black while driving is grounds enough to be pulled over, especially in areas with high crime rates and police presence.

‘It really gets under my skin’

Earlier this year, Treyvon Coulter, a 22-year-old East Oakland resident, was driving down 82nd Avenue with a friend when a police car passed on the other side of the street. A few minutes later, the officer was behind him, lights flashing with backup on the way: Coulter’s brake lights were out.

Officers said they smelled marijuana in the car and cuffed Coulter’s friend while they searched the vehicle. They turned up no drugs, and the two men were sent on their way, Coulter with a ticket in hand.

Encounters like this — traffic stops involving African American motorists turning into discretionary searches — are common. Over the 12 months analyzed by The Chronicle, more than half of all people stopped for traffic violations were black, with 1 in 5 of those stops ending with the driver being searched. White motorists were four times less likely to be pulled over, and those who were stopped were nearly six times less likely to be searched.

“There have been killings and everything like that, and police are taking their precious time writing me a ticket, searching my car?” said Coulter, adding he has been pulled over about 10 times in the past few years. “It really gets under my skin.”

Because the majority of people stopped by police are black, some say African Americans wind up being disproportionately charged with misdemeanors or felony offenses — a trend reflected in Police Department stop data.

“The best analogy is fishing a pond dry,” Glaser said. “If police are mostly looking for crime in certain populations, they’re going to find more of it there, just as if people are fishing only one pond, they’ll only catch fish there.”

East Oakland’s main drag

The most overfished pond, so to speak, is in the flatlands of East Oakland.

The swath of the city between Interstate 580, Lake Merritt and San Leandro is an epicenter for prostitution and violent crime, according to police. It’s also a hot spot for police stops.

Since September 2014, close to 4,000 people were pulled over on the 6.8 miles of International Boulevard, the vast majority black or Latino. More than 250 of the stops on East Oakland’s main drag were predicated on reasonable suspicion, a higher count than on all 22 miles of Broadway, Telegraph and San Pablo avenues, Martin Luther King Jr. Way and MacArthur Boulevard combined.

Just 12.6 percent of the reasonable suspicion stops on International Boulevard ended with someone being booked and charged with a crime, much lower than the citywide average of 19.5 percent. The likelihood officers found drugs, guns or other evidence after any discretionary search was also below the city’s average.

In International Boulevard, some civil rights advocates see signs of geographic — and subsequently racial — profiling.

“It suggests the department is focusing on stopping people of color in this specific, targeted area, and at the same time it’s not resulting in higher levels of catching criminals,” said Chauncee Smith, a legislative advocate at the American Civil Liberties Union of Northern California. “It’s strong evidence of inefficient policing.”

A few factors could skew the numbers. Many of the stops on International Boulevard were vehicle stops, which have lower search-recovery rates, according to police. Also, because the department is intent on reducing crime in East Oakland, it deploys more officers to the area than to other parts of the city. In turn, those officers stop and search more drivers and pedestrians.

“The overwhelming feeling is we need the police in communities of color where violence is most prevalent,” Figueroa said. “But we need them to stop the right people and not go out and stop everybody.”

The Oakland Police Department knows it stops and searches black residents at high rates: The agency is one of few in the nation to gather, analyze and publish reports on who’s pulled over in the city. The department is working with a host of outside experts to try to achieve some sort of parity regarding police stops, which is required before the agency can be freed from federal oversight.

“We’re trying to come up with an appropriate measuring stick that we can all agree on, one that’s fair to our clients, fair to the city and fair to the department,” said Jim Chanin, a civil rights attorney who helped write the Negotiated Settlement Agreement in 2003, which implemented federally mandated reforms at the department.

Profiling or social reality?

Finding the right benchmarks, though, is difficult. What may seem like racial profiling in the numbers could be a reflection of larger social ills, such as high crime rates in parts of the city.

“We haven’t found a magic number, if you will, for analyzing stop data,” Figueroa said. “But we’re finding ways to critically look at the work we’re doing and see if we’re doing it in the most fair and equitable way possible.”

The department is in the precarious position of trying to keep Oakland’s most crime-ridden corridors safe while also not over-policing them, but there are signs of improvement.

Over the past year, Oakland police recovered illegal contraband after performing discretionary searches on drivers and pedestrians 38 percent of the time. During the prior 12 months, the “yield rate” was 24.6 percent.

The number of reasonable suspicion encounters also fell from 2,305 stops to 1,876 over the same time frame, even as the total number of stops increased — a change the Police Department says is deliberate.

Federal monitors have taken notice, commending the department for becoming more precise about who is pulled over and searched in the city. “Officers are thinking more about the (signals) of crime and less about stereotypical behavior,” Chanin said. “There’s no doubt progress has been made, the question is whether or not the department is in compliance.”

The sentiment that African Americans are disproportionately, and perhaps unfairly, targeted for breaking traffic laws or looking suspicious isn’t unique to Oakland. Studies have shown that bias influences everyone, including police.

“Stories of injustice, degradation and humiliation reverberate throughout the community,” said Olis Simmons, president and CEO of the East Oakland community group Youth Uprising. “So every stop, even very well managed by extraordinarily well-trained, seasoned officers, leaves a bad taste.”

While there’s still no consensus on how to address the issue, California is trying to find a solution.

All state law enforcement agencies will soon be required to gather stop data under Assembly Bill 953. The legislation, which was signed by Gov. Jerry Brown in October, will require police departments to track the demographics and outcomes of police stops, then send the information to an office of the state attorney general for analysis.

Reporting stop data

The largest police departments will have to start reporting their stop data in April 2019, and the smallest by April 2023.

Just like body cameras led to reductions in use-of-force at certain police departments — including Oakland’s — legislators hope that by making all police stops public record, officers will be more mindful about whom they pull over.

“We don’t want to hamper their ability to police, but at the same time we need to know if certain areas are being over-policed and others are being under-policed,” said Assemblywoman Shirley Weber, D-San Diego, who wrote the bill. “Once you begin collecting and looking at the data, you can be really proactive about finding a resolution to the problem.”

Joaquin Palomino is a San Francisco Chronicle staff writer. E-mail: jpalomino@sfchronicle.com Twitter:@JoaquinPalomino