It takes time to change social norms, so it'll probably take many, many years until it's as socially unacceptable to text or use a cell phone while driving as it is to start the engine without first buckling a seat belt. In the meantime, researchers say, smart policies are needed to address the increasing share of pedestrian and bicyclist deaths attributed to distracted driving.

According to a new study published in Public Health Reports, the rate of distracted driving-related fatalities per 10 billion vehicle miles traveled went up from 116.1 in 2005 to 168.6 in 2010 for pedestrians and from 18.7 in 2005 to 24.6 in 2010 among bicyclists. However, distracted driving-related deaths among motorists decreased over the same time period — a trend that study authors said mirrored overall motor vehicle fatalities and may be attributed to safer vehicles. Unfortunately, cyclists and pedestrians don't have such protection on the road. In fact, distracted drivers were 1.6 times as likely as nondistracted drivers to mortally hit a pedestrian at marked crosswalks and about three times as likely to hit a pedestrian while on a road shoulder.

"Distraction is becoming more of an issue over time, so it makes sense that we'd see these increases," said study co-author Fernando Wilson, associate professor in the College of Public Health at the University of Nebraska Medical Center. "That wasn't a surprise, but I think the percentage increase was striking, particularly for pedestrian fatalities."

In conducting the study, Wilson and his colleagues used the National Highway Traffic Safety Administration's definition of distracted driving, which can range from texting or using a GPS to eating or drinking, and gathered data from the Fatality Analysis Reporting System from 2005 to 2010. In addition to reporting on fatality rates, the study also examined demographic characteristics among those most at risk of being hit by a distracted driver. Pedestrians involved in distracted driving crashes were mostly male, white and between ages 25 and 64; bicyclist victims were also more likely to be male and white. More than 80 percent of pedestrian victims were hit in a metro area as were more than 77 percent of bicyclists. The majority of both pedestrians and bicyclists included the study were hit outside a crosswalk. Study authors Wilson, Jim Stimpson and Robert Muelleman write:

Mounting evidence links the use of electronic devices with increased traffic deaths and injuries. Even though traffic deaths are declining, deaths from distracted driving are rising, with one study attributing much of this increase to texting volume, which surpassed 100 billion monthly text messages in 2008. However, there are many potential causes of distraction other than electronic devices that threaten roadway safety. Most of this research has examined aggregate fatalities and injuries from distracted driving crashes, but little is known about the characteristics of victims killed in these crashes despite extensive research on predictors of pedestrian injuries.

While the current data on distracted driving is surely enough to act on, Wilson told me the numbers are probably under-reported. There's inconsistency across states and agencies when it comes to reporting the specific causes of distracted driving, and it really comes down to the individual law enforcement officer and whether he or she documents what kind of distraction — a phone call, a text, GPS — was involved in a crash, he said. Also, Wilson added, without quality data it makes it harder to evaluate the effectiveness of interventions.

"Improvement in data collection would definitely be helpful for finding solutions, but that doesn't mean states or localities have to wait to actually create policy," Wilson said. "I don't think anyone is going to argue that the problem is not there and not significant...People may quibble over the numbers or the types of distractions, but I think that everyone agrees that distracted driving is a major threat to road safety."

Right now, the evidence is mixed as to the success of laws that target distracted driving. For example, Wilson said, several studies show that years after the passage of laws that ban texting or cell phone use while driving, such rates go back up to before the law's enactment or don't change at all.

"These policies really need a sustained commitment by law enforcement and sustained media attention to maintain awareness or the effect dissipates," Wilson said. "The policy environment is still a work in progress."

However, the study notes that there is "growing evidence that changing the built environment, which includes traffic engineering and roadway characteristics, is an effective, sustainable approach to protect pedestrians and bicycle riders." Wilson added that although built environment changes can bump up against funding restraints, it's definitely an option policymakers should consider when trying to save lives on the road.

"We want to reach anyone who could glean insight from the study and might be able to use the results in some way, whether that's advocacy for reshaping the built environment, installing more bike lanes, creating marked crosswalks or passing laws to curb distracted driving," he told me. "It's going to take time to reshape social norms to make (distracted driving) unacceptable."

To download a full copy of the Public Health Reports study, click here.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for more than a decade.