The first moments of police interactions with drivers can tell us about what happens next—with officers often giving orders rather than providing reasons for traffic stops, according to a new study that analyzed law enforcement encounters.

Nationwide, the public has highlighted the need for police officers to deescalate routine car stops, where Black drivers are disproportionately pulled over. What makes the findings relevant today is that police reports often lack context about how officers and drivers communicate with each other.

Researchers at the University of Michigan, Virginia Tech University and Stanford University found that stops with escalated outcomes (those ending in arrest, handcuffing or a search) often originate in the earliest moments: the first 45 words spoken by the officer—or 27 seconds.

In stops that result in escalation, officers are more likely to issue commands as their opening words to the driver, and less likely to tell drivers the reason why they are being stopped.

“Now, using police body cams to analyze the interactions, we can see if the officers are transparent in providing the reason for a stop … or whether officers press drivers with accusatory questions or authoritative commands,” said study co-author Nicholas Camp, assistant professor of organizational studies.

Camp and colleagues conducted two studies. In the first one, they analyzed the words used from the police body-worn camera footage from 577 stops of Black drivers for one month in a racially diverse city. An officer’s language early in the stop was indicative of how the encounter may end—even for stops identified as traffic enforcement.

This study showed that police who initially provide justification for a stop earlier rather than later in a stop comports with ideals of transparency and trustworthiness and could bring the tension down. However, officers in escalated stops were 2.5 times more likely not to provide a reason for the stop (38% vs. 15%) and were nearly three times more likely to initiate the stop with an order (22% vs. 8%).

In the second study, researchers exposed more than 180 Black men to audio clips of the same stops to determine how escalated stops are perceived: participants report more negative emotion, appraise officers more negatively, worry about force being used, and predict worse outcomes after hearing only the officer’s initial words in escalated versus non-escalated stops.

Amid calls for police officers to deescalate encounters with Black citizens, researchers said the study sheds light on when and how car stops escalate, as well as the psychological impact on Black men.

The other authors of the study, which appears in PNAS, are lead author Eugenia Rho, assistant professor of computer science at Virginia Tech; Jennifer Eberhardt, professor of psychology and organizational behavior at Stanford University; Dan Jurafsky, professor of computer science and linguistics at Stanford; Reid Pryzant and Maggie Harrington, both graduate students at Stanford; and Yuyang Zhong, U-M research assistant.