Micro Places – Potts (2020)

Study Reference:

Potts, J. (2020, July 20). How do we know it works? Conducting a rapid research police experiment to test the effectiveness of flashing police lights on auto crime. National Institute of Justice, U.S. Department of Justice.

Location in the Matrix; Methodological Rigor; Outcome:

Micro places; General; Proactive; Rigorous; Effective

What police practice or strategy was examined?

This study evaluated the impact of patrols with police lights on (steadily flashing blue, red, and amber lights on a patrol car) in comparison to patrols with police lights off in the Vallejo Gateway Plaza Shopping Center, a known auto theft hot spot in Vallejo, California. During the study period, two patrol cars were assigned to the location for a shift from 12:00 pm to 10:00 pm, operating with lights on or off.

How was the intervention evaluated?

The intervention was evaluated using a randomized controlled trial over a 34-day period from November 23, 2018, to December 28, 2018 (December 24th and 25th were excluded). Days during the trial period were evenly divided into two conditions: lights-on days (intervention) and lights-off days (control), providing a total of 17 days for each condition. Officers were informed of the condition by text message an hour prior to the start of their shift, and compliance with the assigned condition was monitored using random spot-checks. The impact of the intervention was evaluated by comparing the total incident count of auto thefts and auto burglaries that occurred on the days corresponding to each condition. The study also tracked the number of stops, arrests, and motor vehicle registration checks made by individual officers by reviewing data associated with their unique call signals.

What were the key findings?

The author reported that the use of patrol car lights was associated with a 50% reduction in total auto-related crime when compared to the lights-off condition, but this result was not statistically significant. The study did find a significant difference between the conditions in terms of auto thefts: there were zero during the lights-on condition and four during the lights-off condition. With regard to officer activities, the study showed that officers made 68% more motor vehicle registration checks and double the number of arrests during the lights-on condition, though these differences were not statistically significant. There was no significant difference between the two conditions in terms of the average number of daily citizen contacts.

What were the implications for law enforcement?

The author suggests that this study exemplifies how simply improving the visibility of law enforcement in a hot spot via patrol lights may reduce auto-related crime, particularly auto theft. A more observable law enforcement presence may thus be sufficient to have a discernable impact on auto-related crime while avoiding excessive costs or overtime hours. However, the increase in officer activity during the lights-on days may have also contributed to the observed impacts.

Where can I find more information about this intervention, similar types of intervention, or related studies?