Study Key Observations

• On limited-access roads, the share of driving time spent handling a phone rose by 12% for every 5 mph drivers went over the local speed limit. Limited-access roads are freeways and other roads where vehicles enter and exit only via on- and off-ramps.
• On other roads, such as arterials and routes that connect towns, every 5 mph over the local limit was linked to a smaller 3% increase in phone handling. These roads often have traffic lights, intersections, roundabouts and stop signs that require drivers to take action periodically, even when traffic is flowing.
• An alarming relationship
• The increases were larger on roads with higher posted limits. On limited-access roads with 70 mph limits, for example, for every 5 mph a vehicle exceeded the limit there was a 9% larger increase in phone handling than on similar roads with 55 mph limits.
• A similar pattern showed up on roads with more access than freeways. Compared with roads posted at 25 or 30 mph, there was a 3% larger increase in phone handling for every 5 mph drivers exceeded the limit on 45 or 50 mph roads and a 7% larger increase on 55 mph roads.

Some factors Could Be Driving The Pattern

“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 affect 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.
• Previous studies have shown that drivers are more prone to engage in distracting activities when traveling at slower speeds or in simpler traffic settings, adjusting their behavior according to their perception of risk. But these studies did not tell the full story.
• Although some studies looked at road type and traffic, most were limited to a few settings or relied on small groups of volunteer drivers to understand how speeding fit in. In addition, most examinations lumped together the time spent driving normally with the time spent stopped at intersections or in bumper-to-bumper traffic.