Most drivers will give a friendly—or maybe not so friendly—tap on the horn if the motorist in front of them doesn't notice that a traffic light has turned green. The driver may simply be gathering wool and unaware of the change, but in many cases they're focused more on a text message or map than the light.

A new study by the Insurance Institute for Highway Safety suggests that red lights are a prime location for such distracting behaviors. Drivers were most likely to engage in secondary behaviors while stopped at an intersection, and they were least likely to engage in this behavior while in a roundabout.

Researchers observed drivers on four roads in northern Virginia at different times of the day between 2013 and 2014. Nearly 17,000 drivers were observed on a straightaway, roundabout, and at an intersection with a traffic signal. The sites were located close to one another to allow researchers to see how similar groups of drivers acted on different kinds of roads.

Almost one out of every four drivers was observed doing some secondary behavior in addition to driving. At the intersection, 30 percent of drivers engaged in some secondary activity while stopped and 23 percent did so while moving through the intersection.

Straightaways were the second most likely location for secondary behavior, with 24 percent observed doing something in addition to driving. Drivers were least likely to be doing a secondary behavior in a roundabout, although 21 percent were observed doing something else other than driving.

Researchers controlled for a driver's estimated age and gender as well as the community and time of day. They determined that drivers were 41 to 66 percent more likely to engage in a secondary behavior at a red light than they were in other situations. Drivers going through a roundabout were 40 to 73 percent less likely to manipulate a cell phone.

"It makes sense that drivers would be more likely to give their full attention to the road when the driving is more complicated, as in a roundabout," said David Kidd, a senior research scientist at IIHS and the study's lead author. "It seems that some drivers are saving the most demanding tasks like eating, dialing a phone or texting for when they're stopped at a light."

Holding a cell phone but not using it was the most common behavior, with 5 percent of drivers doing so. This behavior was less frequent during stops, with only 2.2 percent of drivers seen holding a cell phone while at the red light. By contrast, it was the most frequent activity at the other sites. A total of 6.3 percent of all drivers held a cell phone while moving at an intersection, 6 percent while in the straightaway, and 4.2 percent while in the roundabout.

Talking on a handheld cell phone was the next most common behavior, with 4 percent of drivers having a phone conversation. This activity was also more prevalent away from the red light, with 4.4 percent talking on a cell phone on the straightaway, 4.2 percent in the roundabout, 4 percent while moving at the intersection, and 3.6 percent while stopped.

Drivers waiting for the red light to change were most likely to be seen eating or drinking, with 5.5 percent seen engaging in this behavior while stopped. Eating or drinking was also seen in 3.3 percent of straightaway drivers, 2.7 percent of drivers moving at the intersection, and 2.6 percent of roundabout drivers.

Drivers were more likely to engage in a number of behaviors while stopped than if they were moving. While 4.3 percent of drivers at the red light were seen talking or singing with a passenger, only 2 percent were seen engaging in this behavior in the straightaway. Another 2.1 percent were seen talking or singing with a passenger while moving at the intersection, while 3.4 percent did so in the roundabout.

This behavior was seen in 3.3 percent of drivers stopped at a red light without a passenger as well as 2.5 percent of drivers in the roundabout. Among straightaway drivers, 1.8 percent were seen talking or singing without a passenger while 1.7 percent of drivers moving through an intersection were talking or singing to themselves.

Manipulating a cell phone, for behaviors such as texting or using a smartphone app, was most common at the red light and least common in the roundabout. A total of 3.8 percent of drivers manipulated a cell phone while stopped at an intersection, compared to 1.2 percent of roundabout drivers, 2.7 percent of drivers moving at an intersection, and 2.8 percent in the straightaway.

Smoking was also more common at a stop, with 2.6 percent of drivers lighting up at a red light. Only 1.7 percent of drivers moving through an intersection, 1.6 percent of roundabout drivers, and 1.4 percent of straightaway drivers were seen smoking.

Grooming was a rare behavior, observed in 0.5 percent of straightaway drivers, 0.2 percent of drivers moving at the intersection, and 0.1 percent of roundabout drivers. The behavior was more common during stops, with 1.3 percent of drivers stopped at an intersection doing some kind of grooming.

Less common activities included wearing headphones or earbuds, wearing a Bluetooth device, manipulating an in-vehicle system, or manipulating or holding a device other than a cell phone.

Distracting behaviors are often discouraged at red lights as well as while the vehicle is moving. John Hilkevitch and Lauren Zumbach, writing for the Chicago Tribune, say texting or using a cell phone while waiting at a red light can cause a driver to make a "jackrabbit start" or erratic maneuver when they see that the light has turned green. This behavior may also lead to road rage incidents or disrupt traffic flow by allowing fewer cars to get through an intersection or causing a sensor on a traffic signal to think that the street has cleared.

In several communities and states, including Connecticut, texting or using a handheld cell phone while driving is entirely forbidden. This means that even if you are at a red light and have your foot on the brake, it is illegal to use your phone while you wait.