License plate recognition (LPR) technology is a vehicle-scanning device deployed by law enforcement to detect wanted vehicles (such as those reported stolen or missing). Originating in the United Kingdom in the 1980s, LPR has been used predominantly to combat auto theft, although it has also been used to detect wanted vehicles associated with other types of crime, such as known vehicles of at-large suspects. Because LPR can collect and store the dates, times, locations, and plate names of cars in its range, it can also be used to locate individuals or offenders based on previously collected data as well as confirm a suspect’s alibi or whereabouts at a particular place and time.
Prior to the advent of LPR, police officers had to go through the lengthy process of determining whether a vehicle was suspicious based on their discretion, calling the dispatcher, and then waiting to see if the license plate matched one of the wanted vehicles in the database. LPR automates this manual approach and also reduces the use of officers’ discretion in deciding which tags to run since all tags within view are scanned. Some LPR systems can scan up to four lanes of traffic and read 8,000-10,000 plates in just one shift.
LPR consists of infrared cameras that are normally mounted on police cruisers (although they can also be attached to a fixed location, such as a toll plaza). As civilian cars pass, the cameras capture the unique reflective material of the license plates in a photo. The photos are then run through character-recognition software to determine the exact numbers and letters of the plates. Nearly simultaneously, the plates are checked against a “hot list” of vehicles in the state; a signal to law enforcement is triggered when a car is of interest. The officer then verifies the accuracy of the hit by looking at the numbers and letters on the plate before taking any action.
Lum and colleagues (2011) found no significant difference in the levels of all crime between the experimental license plate recognition (LPR) hot spots and control (no LPR) hot spots during the intervention period and 30 days after. This suggests that deployment of LPR did not have a general deterrent effect on all crimes.
Auto Theft/Theft From Auto and Auto-Related Crimes
There were also no significant differences between the LPR hot spots and control hot spots on auto theft or auto-related crimes during the intervention period and 30 days after. This suggests that deployment of LPR did not have an offense-specific deterrent effect either.
Taylor, Koper, and Woods (2012) found no statistically significant differences between the LPR group, the manual plate checking group, or the normal patrol control group based on calls for services (CFS) for vehicle theft during the intervention weeks and during the 2 weeks immediately following the intervention. The multivariate analysis showed that the routes with the manual plate checking saw a statistically significant 75 percent decline in the odds of having a CFS for vehicle theft versus the control group routes, although the effect faded over time. There was no significant change noted for the routes with the LPR.
During the intervention weeks, there were also no statistically significant differences between the groups on vehicle theft based on Uniform Crime Report (UCR) data. However, during the 2 weeks postintervention, there was a statistically significant difference observed. The routes with the LPR had a slightly higher number of vehicle thefts compared to the routes with the manual plate checks or control group routes. Multivariate analysis of the UCR data revealed results similar to those found based on analysis of the CFS data. There was a statistically significant 74 percent reduction in the odds of a UCR-reported vehicle theft in the manual plate check routes versus the control group routes; however, again the effect faded over time. There was no significant effect noted for the routes with the LPR.
Recovery of Stolen Vehicles
There was a small, statistically significant difference in the number of recoveries for occupied stolen vehicles between the LPR and manual plate check routes, but no significant difference in the number of recoveries of unoccupied stolen vehicles between the two routes. The routes with the LPR had four recoveries for occupied stolen vehicles compared to zero recoveries for the manual plate check routes (a statistically significant difference). The routes with LPR also had six recoveries for unoccupied stolen vehicles compared to five recoveries for the manual plate check routes (a nonsignificant difference).
Again, there was a small, yet significant difference in the number of arrests for stolen vehicles between the LPR and manual plate check routes, but there was no significant difference in the number of arrests for stolen plates between the two routes. The routes with the LPR had three arrests for stolen vehicles, compared to zero arrests for the manual plate check routes (a statistically significant difference). The routes with the LPR also had one arrest for stolen plates compared to zero arrests for the manual plate check routes (a nonsignificant difference).