When IIHS' test program was being developed, research showed that front-crash prevention systems that performed best at 12 and 25 mph also did well at higher speeds. However, Kidd's study found that only 3 percent of police-reported rear-end crashes happened on roads with speed limits at 25 mph or under.
More specifically, about 43 percent of the police-reported rear-end crashes and 12 percent of fatal rear-end crashes occurred at or below speeds of 45 mph, the study found.
Additionally, the study found nearly 70 percent of fatal rear-end crashes occurred on roads where the speed limit is 55 mpg or higher. But about half of nonfatal rear-end crashes happened on roads with speed limits from 35 to 45 mph.
The study used federal databases of fatal and police-reported crashes to identify certain rear-end vehicle-to-vehicle crashes from 2016 to 2019 and relied on posted speed limits as well as information from the event data recorders as indicators of the striking vehicle's speed before the crash.
Based on the findings, IIHS said it planned to conduct research tests on six vehicles equipped with different automatic emergency braking systems at speeds up to 45 mph. The tests will be conducted with different types of passenger vehicles as well as motorcycles and medium- and heavy-duty trucks as the stationary vehicle.
IIHS introduced its vehicle-to-vehicle front crash prevention test in 2013 and required a "basic, advanced or superior" rating for vehicles to earn a 2014 Top Safety Pick+ award.
With 85 percent of 2022 model-year vehicles evaluated by IIHS so far earning a "superior" rating in the test, IIHS determined it "no longer effectively differentiates among systems" and is dropping the rating from its award criteria in 2023.
The institute said Kidd's study was a "first step" in determining whether the test should be replaced.
At least 12 automakers already have met a 2016 voluntary commitment brokered by the institute and NHTSA to equip at least 95 percent of their light-duty cars and trucks with automatic emergency braking. The commitment calls for automakers to meet the benchmark for models manufactured from Sept. 1, 2022, to Aug. 31, 2023.
In February, the institute said it also planned to release a new nighttime test and rating system for automatic emergency braking this year that will become part of the criteria for the 2023 Top Safety Pick and Top Safety Pick+ awards.