Almost half of all drivers whose vehicle included a lane departure system had this feature turned off during their normal commuting, according to a recent analysis by the Insurance Institute for Highway Safety.

The organization found that the lane departure system had been turned off in 49 percent of vehicles brought in for servicing. This rate of usage was considerably lower than other safety features, which were activated in about nine out of 10 vehicles.

Lane departure systems are defined as any feature meant to prevent a vehicle from drifting out of its lane. These systems may include warnings to alert the driver that they are leaving the lane, automatic steering or braking to stop a vehicle from leaving a lane, or continuous steering input.

IIHS previously looked at the issue of lane departure system usage in a study released in January 2016. Only one-third of the 184 Honda models brought in for servicing in that study had their lane departure systems turned on, while all but one had their forward collision warning activated.

The most recent study expanded to observe driver habits on models from nine automakers. The lane departure systems in the observed vehicles remained on or off depending on the last trip instead of defaulting to one of the settings at the start of each trip.

Fifty-one percent of the 938 vehicles brought in for servicing had their lane departure warning activated. By comparison, nearly every vehicle—99 percent—had a blind spot monitoring system turned on. There were also high rates of use for rear cross-traffic alerts (97 percent), front crash prevention (93 percent), and driver monitoring alert (90 percent).

Drivers were more likely to turn off the lane departure system if it used auditory warnings. Only 46 percent had the system activated if it issued an audible alert, while 54 percent had it turned on if it used tactile warnings. In surveys issued to the vehicle owners, those who turned off the lane departure system typically said they considered it distracting and unnecessary.

"Depending on the way you drive, lane departure warnings can go off fairly frequently in the course of regular driving, even when there is no imminent danger," said Ian Reagan, a senior research analyst at IIHS and lead author of the study. "Systems that beep seem to annoy people more than systems that warn the driver with vibrations of the seat or steering wheel."

Lane departure systems were also more likely to be activated if they actively guided a vehicle back into a lane instead of simply issuing a warning. Several models allow drivers to turn off the feature with the push of a button, but drivers were less likely to turn off the lane departure system if it required a more complex process to deactivate. The Volvo XC90 requires drivers to navigate a menu to shut off the feature, and 86 percent of this model's owners kept the system activated.

An IIHS study in 2010 estimated that lane departure systems could prevent or reduce the severity of approximately 23 percent of fatal crashes. It also said a simple warning may be inadequate in some scenarios, since about one-third of lane departure crashes involve driver incapacitation. If a driver falls asleep or is otherwise incapacitated, they may not be able to effectively respond to a warning and take control of the vehicle.

The organization says lane departure systems haven't been able to reduce insurance claims, and that the low usage rates may be one reason for this trend. However, IIHS also says a forthcoming study indicates that lane departure systems have been effective in preventing more severe crashes caused by vehicles drifting out of a lane.