A new study suggests that while a significant number of teenage drivers text while driving to respond to a parent's message, they often do so because they inaccurately think that the parent expects a quick reply.

The study, commissioned by Liberty Mutual Insurance and the organization Students Against Destructive Decisions, found that 48 percent of the teenage drivers polled said they are more likely to text and drive when they are alone in a vehicle. The most frequent reason for doing so was to send an update to a parent, with 55 percent saying they had sent a text message while driving for this reason.

Twenty-five percent said they believe a parent expects a reply to a message within five minutes, and 19 percent thought the parent who sent the message would expect a reply within one minute. However, 58 percent of the parents questioned in the survey said they do not have any set expectations for when their child would reply to a text message.

Previous studies have also suggested that young drivers often engage in distracting behaviors in order to stay in contact with their parents. The American Psychological Association says a 2014 analysis of 400 teenage drivers found that more than half of them had talked with a parent on a cell phone while driving.

A 2013 survey by Liberty Mutual Insurance and Students Against Destructive Decisions found that half of the participating teenage drivers had spoken with a parent on a cell phone while driving. Respondents were more likely to text friends than their parents. However, 16 percent of the 18-year-olds and 8 percent of respondents between the ages of 15 and 17 said they had texted a parent while driving.

According to the National Highway Traffic Safety Administration, 424,000 people were injured and 3,154 people were killed in crashes caused by distracted driving in 2013. Teenagers had the largest proportion of distracted drivers, and 10 percent of drivers under the age of 20 were reported to be distracted at the time of the crash.

The National Parent-Teacher Association says parents should set a good example for teenagers by avoiding distracting behaviors while driving. The organization also recommends that parents avoid calling or texting their child when they might be driving.

Students Against Destructive Decisions says parents and teenagers should have a conversation about the dangers of distracted driving. A parent-teen driving contract can outline the expectations for safe driving as well as the consequences for violating these rules.

The National PTA says one way to demonstrate the risks of texting while driving is a "commentary drive." In this exercise, the parent drives through an unfamiliar area while the teenager rides as a passenger, sends and reads text messages, and describes what they see on the road and how they would respond. Parents should point out hazards the teenager is missing or slow to respond to.

The most recent survey suggests that a significant share of teenage drivers also make risky decisions in an attempt to stay connected with friends. Eighty-eight percent of the respondents who considered themselves to be safe drivers admitted to using a smartphone app while driving. Thirty-seven percent said they have texted while driving to confirm or coordinate event details, and 34 percent said they take their eyes off the road when they receive a notification from a smartphone app.

The largest share of teenage drivers said they have used Snapchat on the road, with 38 percent saying they have checked this app while driving. Twenty percent said they have used Instagram, 17 percent said they have used Twitter, and 12 percent each said they have used Facebook or YouTube.

"Today's hyper-connected teens' 'fear of missing out' can put young drivers at risk on the road as they may be more plugged into their devices than the actual driving task," said William Horrey, principal research scientist at the Liberty Mutual Research Institute for Safety. "Teens may be at higher risk because they don't always have the attentional capacity to deal with all the complexities on the road. These distractions in addition to fatigue may be even more significant with teens due to their relative driving inexperience as well. It's so important for parents and teens to recognize and talk about these dangerous distractions to ensure better safety behind the wheel."

The study indicates that teenage drivers are also at a significant risk for drowsy driving. Fifty-six percent of respondents said they have fallen asleep or nearly fallen asleep while driving. Seventy percent admitted to driving while fatigued.

Although 61 percent of the parents surveyed said they thought their child gets enough sleep, 52 percent of teenagers in the study said they get less than six hours of sleep a night. Fifty-one percent of parents who said they don't think their child gets enough sleep thought it was because they stayed up late using their smartphone.

The teenagers included in the survey were more likely to blame a lack of sleep on a busy schedule, with 43 percent saying extracurricular activities affected their sleep cycle. Thirty-two percent said they stayed up late to finish homework, and 20 percent said they worked late hours. Twenty-four percent said they did not get enough sleep because of social activities, and 10 percent said they were fatigued from partying the night before.

"Today's parents are juggling their own busy schedules, and too often young drivers' risky habits go unrecognized," said Stephen Gray Wallace, senior advisor for policy, research and education at Students Against Destructive Decisions. "It's critical that parents focus on pinpointing these dangerous driving habits early on—from drowsy driving to technology use behind the wheel—and have frequent conversations with their children about what safe driving really means."

The study was commissioned by Liberty Mutual Insurance and Students Against Destructive Decisions and conducted by ORC International. Focus groups were held in Chicago, Illinois and Washington, D.C. in October, and a nationwide sample of 1,622 high school juniors and seniors was surveyed. The study also polled 1,000 parents of teenage drivers who were in high school.