Drivers are more likely to use their phones while speeding, a tendency that increases crash risk by combining two dangerous behaviors, according to a new study from the Insurance Institute for Highway Safety (IIHS).

“Until now, safety experts believed drivers used their cellphones most at slower speeds,” said IIHS President David Harkey. “But data from safe-driving apps show that, in free-flowing traffic, the opposite is true.”

Excluding time spent stopped at intersections, mired in traffic and driving small neighborhood streets, the amount that drivers handled their phones increased the more they exceeded the speed limit, a nationwide analysis of cellphone data showed.

The study found increases were larger on roads with higher posted limits. On limited-access roads with 70 mph limits, for example, for every five mph a vehicle exceeded the limit there was a 9% larger increase in phone handling than on similar roads with 55 mph limits.

“It’s alarming that the relationship between cellphone manipulation and speeding was the strongest on roads with the highest speed limits,” said Ian Reagan, the IIHS senior research scientist who wrote the study.

Reagan said several factors could be driving the pattern:

  • One possibility is that drivers who take more risks are both more likely to speed and more likely to use their phones.
  • Another is stress: Earlier research shows phone use spikes during rush hour and school drop-off, and those same situations may also lead people to speed.
  • Drivers may also respond to other road cues, such as lighter traffic, an absence of pedestrians or longer gaps between stoplights, on roads with higher speed limits.

The IIHS said the results showed that pairing anti-speeding efforts with anti-distracted-driving efforts could have a bigger payoff, especially in higher-speed zones on limited-access roads.

The organization said common ways to enforce cellphone bans – such as posting officers at intersections or using unmarked vans or buses to look into vehicles – can be more challenging on highways and freeways, which it said supported the case for safety cameras that can monitor both speeding and phone use.

The IIHS also pointed to recent research showing that safe-driving apps can reduce speeding and phone handling by offering lower premiums when drivers avoid those behaviors.