Drivers more likely to use phones at higher speed limits, IIHS study finds

In a new report, the IIHS states: “Until now, safety experts believed drivers used their cellphones most at slower speeds,” said IIHS President David Harkey in a press release introducing the study. “But data from insurance companies’ safe-driving apps show that, in free-flowing traffic, the opposite is true.”

Insurance apps, which promise cost savings to drivers who opt in and demonstrate safe driving behaviour, provided the IIHS with highly nuanced data. The institute explained that these applications use phone sensors and GPS to track speed, hard acceleration, and braking, along with location data, to create a summary that can be analysed to assess driving patterns.

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Drivers’ phone use was determined based on significant device rotation recorded by the gyroscope in the phone. Vehicle speed was calculated by matching GPS data with speed limit databases.

IIHS researchers analysed nearly 600,000 trips taken between July and October across all U.S. states, except Alaska, California, Hawaii, and New York. The study focused on driver behaviour in free-flowing traffic; periods where vehicles were travelling 5 mph or more below the posted speed limit were excluded.

The Findings

Using this methodology, researchers found that phone use increased by 12% for every 5 mph drivers exceeded the speed limit on limited-access highways. On other roads, phone use rose by a smaller 3% for every 5 mph over the limit. The data also showed that drivers were more likely to use their phones on roads with higher speed limits.

On limited-access highways with a 70 mph speed limit, researchers observed up to a 95% increase in phone use as speeds rose above the limit. On other roads, the increase remained closer to 3%.

The findings suggest that factors such as stress, previously linked to increased phone use may play a role. Additionally, roads with higher speed limits may present simpler driving conditions, potentially encouraging more phone use despite the higher speeds.

The IIHS recommends pairing anti-speeding messaging with warnings about distracted driving to address the correlation between the two. While speed cameras can help enforce speed limits, regulating phone use on highways remains more challenging. The research forms part of insurers’ broader efforts to promote safer driving and reduce premiums.