For years, safety researchers believed that drivers were most likely to reach for their phones in slow-moving traffic — stop-and-go conditions that left them bored, impatient and reaching for distraction. A sweeping new study has turned that assumption on its head. Drivers are actually more likely to handle their phones the faster they go, according to research published Monday by the Insurance Institute for Highway Safety. The finding, drawn from nearly 600,000 trips taken by drivers across the United States, suggests that two of the most dangerous behaviors on American roads are not random and independent — they are linked, and they tend to peak at the same moment. “Until now, safety experts believed drivers used their cellphones most at slower speeds,” said David Harkey, the institute’s president. “But data from insurance companies’ safe-driving apps show that, in free-flowing traffic, the opposite is true.” The Numbers Behind the Pattern The study, conducted by IIHS senior research scientist Ian Reagan and senior statistician Sam Monfort, analyzed trip data collected between July and October 2024 by Cambridge Mobile Telematics, a platform provider that powers safe-driving apps used by auto insurers. The researchers focused exclusively on time spent driving in free-flowing conditions, setting aside periods stuck at intersections, idling in congestion or traveling below the posted speed limit — isolating, in other words, the moments when a driver is truly in motion. What they found was a consistent and troubling gradient. On limited-access roads — freeways and highways where vehicles enter and exit only via on- and off-ramps — the share of driving time spent handling a phone rose by 12 percent for every 5 miles per hour a driver exceeded the posted limit. On arterials and other roads with traffic lights and intersections, the increase was smaller but still present: 3 percent