ALPR Effects on Crime and Case Clearance

What the evidence says

All claims on this page come from one source: a 2025 review by Cynthia M. Lum. It summarizes primary studies by Lum and colleagues, Koper and colleagues, Ozer, and Koper and Lum. The review says only "a handful" of methodologically rigorous evaluations (experimental, quasi-experimental and econometric) of automated license plate readers (ALPRs) exist. It reports that many of them are equivocal or show limited effects on crime outcomes, even in realistic contexts.

The strongest evidence is a randomized experiment on crime itself. Thirty-minute patrols in ALPR-equipped cars, run once every few days in randomly selected high-crime places for two to three months, did not reduce auto-related or other crime compared with control locations. The same experiment found no measured difference in initial or residual deterrence between ALPR and non-ALPR patrol visits to high-crime places. The measured crime effect of ALPR patrols is therefore null. The sources do not say whether more patrol time or a different deployment would change that.

Evidence on enforcement outputs points the other way, but it is weaker and associational. Koper and colleagues (2022) found that ALPRs may increase stolen vehicle recoveries but not necessarily arrests of the people stealing cars. In Cincinnati, Ozer (2016) found ALPRs associated with more follow-up arrests per month for violence and property crimes after implementation. Ozer's effect on crime deterrence was unclear. The sources give no mechanism beyond ALPRs producing leads for officers. They do not separate that lead generation from any deterrent effect.

For case investigation, Koper and Lum examined actual case records. Case clearance occurred in about 19% of cases in which ALPRs were used. That is about 1% of the cases they examined. For almost three-quarters of the cases where ALPR use was noted, ALPRs did not contribute in any meaningful way to resolution. The authors believed that more frequent and systematic use in serious investigations could potentially improve case resolution. That is their belief, not a measured result. The case-record analysis is observational, so it cannot isolate ALPR's causal contribution from other investigative work.

Several outcomes people expect to see covered have no direct measurement here. No claim reports a dose-response relationship, a cost per case cleared, or a crime effect for ALPR use in investigations as opposed to patrol.

Where the evidence splits

No contradictions in the current sources.

Thresholds and dose-response

No threshold established in the current sources.

Open empirical questions

• Does heavier or differently targeted ALPR deployment, or confirmed adequate hot spot patrol dosage, change crime outcomes that the tested patrols did not?
• How much of the observed rise in arrests after ALPR adoption is deterrence and how much is lead generation? The sources cannot separate them.
• Does more frequent, systematic ALPR use in serious crime investigations raise case clearance? The sources report this only as the authors' belief.
• Do the findings hold beyond the cities and agencies studied? All claims here come from a single review of a handful of studies.