Clothing that makes pedestrians stand out to human drivers may make them invisible to automated crash prevention systems, according to a new study from the Insurance Institute for Highway Safety (IIHS).

Past IIHS research has shown that, in general, pedestrian automatic emergency braking (AEB) systems reduce the rate of pedestrian crashes of all severities by 27%. However, on dark roads, the effect of pedestrian AEB on crash risk is negligible.

“These results suggest that some automakers need to tweak their pedestrian automatic emergency braking systems,” said IIHS President David Harkey. “It’s untenable that the clothes that pedestrians, cyclists and roadway workers wear to be safe may make them harder for crash avoidance technology to recognize.”

Researchers conducted multiple trials with an adult-sized dummy clothed in a black sweatshirt and pants, a retroreflective jacket with black sweatpants, the black sweatshirt and sweatpants with retroreflective strips added on the dummy’s limbs and joints, and a white sweatshirt and pants.

The tests were run at 25 mph with no roadway lighting, with 10 lux of illumination in the crosswalk or with the federally recommended 20 lux of illumination in the crosswalk. The dummy crossed the track perpendicular to the path of the vehicle in all scenarios.

“The placement and motion of reflective strips on the joints and limbs of pants and jackets allows drivers to quickly recognize the pattern of movement as a person,” said study author David Kidd, a senior research scientist at IIHS. “Unfortunately, the moving strips didn’t have the same effect for the pedestrian AEB systems we tested and probably confounded their sensors.”

IIHS President David Harkey  called it a “worrisome blind spot,” adding: “To make good on their potential, pedestrian detection systems have to work with the other commonly used safety measures.”