Why laptops should be screened separately when conventional x-ray screening is used

Security screening at airports is a highly relevant topic for more than a decade. Large amounts of money are still being invested to continuously improve the efficiency and effectiveness of passenger and baggage screening processes. State-of-the-art x-ray screening machines provide good quality images with high resolutions. Yet, the detection of prohibited items remains a challenging task for screening officers (screeners) and becomes even more difficult when dense electronic devices, such as laptops, are contained in baggage. Due to their compact construction, laptops can easily conceal other parts of luggage or could be used to hide threat items. International and national regulations specify that laptops need to be taken out of passenger bags at security checkpoints for x-ray screening, sometimes causing lower passenger throughput and even annoyance among passengers. The aim of this study was to investigate how leaving laptops inside passenger bags actually affects detection performance of x-ray screening officers, when state-of-the-art technology providing single-view images is applied. The experiment was conducted with 40 certified screening officers from an international European airport. Participants were divided into two experimental groups. Both groups conducted an image interpretation test containing bags and laptops. For the first group, images of bags and laptops were displayed separately, while for the second group, laptops were left inside the passenger bags and displayed as one image. All participants had to judge whether the displayed bags and laptops contained a threat item or not. Threat items of four different categories were used: guns, knives, improvised explosive devices (IEDs) and others (e.g. electronic shock devices). Detection performance (A') and reaction times were measured. A highly significant difference in detection performance between both groups was observed. Throughout all analyses, detection performance scores were much higher when bags and laptops were x-rayed separately. Largest differences were found for the category IEDs. Altogether, the results imply that when no automatic threat detection and only single view images are available, the detection of prohibited items is still far more reliable when bags and laptops are screened separately.