Incident 245: Unverified Misreading by Automated Plate Reader Led to Traffic Stop and Restraint of an Innocent Person at Gunpoint in California

Description: In San Francisco, an automated license plate reader (ALPR) camera misread a number as belonging to a stolen vehicle having the wrong make, but its photo was not visually confirmed by the police due to poor quality and allegedly despite multiple chances prior to making a traffic stop, causing an innocent person to be pulled over at gunpoint and restrained in handcuffed.
Alleged: Unknown developed an AI system deployed by San Francisco Police Department, which harmed Denise Green.

Suggested citation format

Dickinson, Ingrid. (2009-03-30) Incident Number 245. in Lam, K. (ed.) Artificial Intelligence Incident Database. Responsible AI Collaborative.

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We recently covered a story about a lawyer who found himself approached by cops with guns drawn after an automatic license plate reader misread a single character on his plate as he drove by. The police did make an attempt to verify the plate but were stymied by heavy traffic. Unfortunately, it appears they decided to force the issue rather than let a potential car thief escape across the state line.

As I pointed out then, the increasing reliance on ALPRs, combined with the one-billion-plus records already in storage and the millions being collected every day, means the number of errors will only increase as time goes on — even as the technology continues to improve. This person was lucky to escape with nothing more than an elevated heart rate. Others won’t be so lucky… like Denise Green of San Francisco.

Green’s civil rights lawsuit has just been reinstated by Ninth Circuit Court of Appeals, which overturned an earlier decision that granted summary judgment in favor of the San Francisco Police Department. The lower court found that the officers had made a “good faith, reasonable mistake” when they performed a felony stop of Green, which included being ordered out of her vehicle and onto the ground at gunpoint and held in cuffs for nearly 20 minutes while officers verified the plates and filled out paperwork.

The Appeals Court disagreed with this finding and the opinion details what the SFPD is supposed to do with ALPR “hits” and compares this to what was actually happened.

It is undisputed that the ALPR occasionally makes false “hits” by misreading license plate numbers and mismatching passing license plate numbers with those listed as wanted in the database. Because of the known flaws in the system, SFPD officers are trained that an ALPR hit does not automatically justify a vehicle stop, and SFPD directs its officers to verify the validity of the identified hit before executing a stop.

Patrol officers are instructed to take two steps to verify a hit before acting on an ALPR read. The first step is to visually confirm the license plate (to ensure that the vehicle actually bears the license plate number identified by the camera); the second step is to confirm with the system that the identified plate number has actually been reported as stolen or wanted.

The opinion notes that the SFPD, at the time of the incident, actually had no official verification policy in place that designated which officer(s) should perform this task. The expert testifying on behalf of the PD indicated that it would most likely be performed by the operator of the “camera car” (the vehicle with the ALPR) but was unable to point to any policy actually stating this.

So, there’s one level of failure. It could be that all of the officers involved (at least four, according to court documents) thought someone else had handled the verification. That would be an “honest mistake,” but that shouldn’t allow the department to escape being held accountable for its lack of clear verification procedures.

On the night of March 30, 2009, Appellant Denise Green, a 47-year-old African-American woman with no criminal record, was driving her vehicle, a 1992 burgundy Lexus ES 300 with license plate number 5SOW350, on Mission Street in San Francisco. At approximately 11:15 PM, Green passed a police cruiser equipped with an ALPR operated by SFPD Officers Alberto Esparza and Robert Pedersen. When Green drove past Esparza and Pedersen’s camera car, the ALPR misread her license plate number and identified her plate as belonging to a stolen vehicle. It was late and dark outside, which rendered the ALPR photograph blurry and illegible. As a result, Officer Esparza could not read the ALPR photograph, nor could he get a direct visual of Green’s license plate.

Esparza was currently involved in an arrest, so he radioed in the hit. He identified the vehicle as a dark Lexus with the plate number 5SOW750, one digit off from Green’s actual number. Dispatch ran the number and found that the plate belonged to a stolen gray GMC truck. The opinion notes that Esparza never bothered to inform dispatch that he had not verified the plate number himself and was working from a lousy ALPR photo.

Sergeant Kim was in the area and heard the radio traffic linking the plate (5SOW750) to a grey pickup and Esparza’s observance of a dark Lexus. Kim had plenty of chances to clear up the misidentified plate, but he never did so.

Sergeant Kim saw that the first three numbers of Green’s license plate matched the plate read over the radio, but he did not visually identify all seven numbers on Green’s license plate. He also radioed Officer Esparza for a description of the vehicle, and Officer Esparza confirmed that the vehicle he saw was a dark burgundy Lexus. Sergeant Kim then decided to make a “high-risk” or “felony” stop…

Because Sergeant Kim believed that Green posed a risk, he waited for backup before pulling her over. While he waited, he followed her vehicle for a brief amount of time and, at one point, even stopped behind her at a red light. At no point while he was following or stopped behind Green’s vehicle did Sergeant Kim visually confirm the entirety of Green’s license plate number, even though nothing obscured his ability to do so. Furthermore, Sergeant Kim did not confirm Green’s plate number with dispatch, but he did hear Officer Esparza inquire whether the vehicle with the plate number 5SOW750 was stolen. Sergeant Kim admits that if he had read the full plate, he would not have had the reasonable suspicion to effect the stop.

But the stop was made and Green was approached by at least four officers with weapons drawn. She was restrained, cuffed and held while the SFPD officers finally got around to verifying the plate number on her vehicle.

The SFPD, while fighting Greene’s Fourth Amendment claims, chose to spin Officer Esparza’s lack of verbal confirmation that he had personally observed the plate (rather than the ALPR’s lousy photo) as a credible, non-verbal assertion that could “reasonably” prompt other officers into action. Sergeant Kim took Esparza’s lack of information to be an affirmation of his visual verification of Greene’s plate, giving him the reasonable suspicion to effect the stop. The court approaches this argument from another angle, stating that Esparza’s lack of confirmation should have been an indication that Kim needed to perform additional verification.

Because of the SFPD’s lack of clear policy and the Officer Kim’s willingness to believe Esparza’s unstated claims, the officers effected a felony stop based on very little information and a whole lot of belief. Neither of these are enough to rise to the level of “reasonable suspicion,” and certainly not enough to justify the amount of force deployed — especially considering Greene was “physically unthreatening” and compliant during the whole stop.

Once again, we see law enforcement deploying technology without guidelines for usage. (We also see Sgt. Kim’s reluctance to spoil a felony stop by actually reading a license plate that was directly in front of him for several minutes…) Many police departments tend to prefer unsupervised tech, an attitude that is increasingly resulting in policy being set by lawsuit. Abuse first, settle later, and lastly, institute guidelines. It’s a hell of a way to “enforce law,” when everyone’s being policed but the police.

Another Bogus Hit From A License Plate Reader Results In Another Citizen Surrounded By Cops With Guns Out