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Status Report, Vol. 52, No. 6 | August 23, 2017 Subscribe

Alerts boost teen drivers' turn-signal use

Warning systems help teen drivers improve their turn-signal use and stay in their lanes, but they don't seem to discourage tailgating.

Crash avoidance warning features help teenage drivers improve their turn-signal use and stay in their travel lanes but appear to increase the time they spend following vehicles at close distances, new IIHS research indicates.

Crash avoidance systems monitor driver input and the environment around the vehicle and warn the driver of a potential collision. The systems could be especially beneficial to young beginning drivers. Real- time feedback on their driving could help teens develop safer habits (see "Monitoring devices let parents supervise new drivers more closely," May 7, 2009).

To explore this possibility, IIHS undertook a naturalistic driving study with the University of Michigan Transportation Research Institute and Honda. The study is the first to evaluate how novice drivers respond to warnings from crash avoidance systems.

Forty 16-17-year-old teenagers who had been licensed for about six to nine months were recruited from Michigan high schools to drive instrumented Honda Accords with crash avoidance technologies. These included forward collision warning, lane departure warning, blind spot monitoring and curve speed warning. Sensors captured information about vehicle movement and driver inputs, and cameras recorded views both inside and outside the car.

Researchers examined whether the warning systems altered teens' driving in terms of headway maintenance, lane keeping and turn-signal use, and whether any changes were sustained after warnings were disabled. They also looked at distraction.

The 20 teens in the experimental group drove for a three-week baseline period with all crash warnings disabled, an eight-week treatment period in which they received crash warnings and a three-week post-treatment period with warnings disabled again. The 20 teens in the control group drove a fully instrumented car for 14 weeks but never received any crash warnings. Data were collected during a 14-month period from late July 2011 to October 2012. When warnings were disabled, the cars continued to collect data on all events that would have prompted alerts.

Teens drove more than 90,000 miles and logged about 10,000 events that triggered warnings. Seventy-three percent of the warnings were for lane drifts, often because the driver failed to signal an intentional lane change. Forward collision alerts accounted for 8 percent of all warnings logged.

After the baseline period, forward conflicts increased for teens in both the experimental and control groups, possibly reflecting their growing comfort with the study cars or acclimation to driving in general. The similar behavior by both groups may be because the experimental driver group may have ignored warnings after getting a large number of false alerts. The Hondas were outfitted with a prototype forward collision warning system that wasn't necessarily representative of market technology. The system had the highest rate of false warnings of the three technologies.

"We didn't find evidence of safety benefits from forward collision warning," says Jessica Jermakian, a senior research engineer for IIHS and the study's lead author.

"During the treatment period, the teens actually spent more time following vehicles closely. Once the forward collision warning system was disabled, they backed off. This might indicate that the drivers were relying on the warning system to let them know when they should brake."

Lane departure warning and blind spot monitoring changed behavior in more positive ways. When drivers received warnings, unsignaled lane departures fell by more than a third. This could indicate higher turn-signal use. Once the warnings were disabled, the proportion of unsignaled lane changes rose but remained about 75 percent lower than during the baseline period, suggesting lingering benefits. The increase in turn-signal use is consistent with prior surveys (see "Dodge/Jeep and Toyota owners say they like their crash avoidance features," March 13, 2014).

The researchers didn't find any evidence that the teens engaged more in secondary tasks, such as talking to a passenger or using phones, when warnings were active. A separate study by IIHS and UMTRI specifically examined distraction among these teens and a group of adults. Having the warning system activated didn't make the drivers more or less likely to engage in secondary behaviors (see "Warning systems neither curb driver distraction nor worsen it," Nov. 17, 2016).

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