IIHS Examines Driver-Assistance Features in Real-World Tests

After performing several Level 2 tests, the Insurance Institute for Highway Safety moves toward a consumer rating system for ADAS.


By Murray Slovick, Contributing Editor

With all of the talk about self-driving cars, an obvious question arises: “How well do the current range of semi-autonomous advanced driver-assistance systems (ADAS) work?”

Trying to find the answer, the Insurance Institute for Highway Safety (IIHS) tested five models from Tesla, Mercedes, BMW, and Volvo on a track and public roads. The five vehicles evaluated were:

  • A 2017 BMW 5-series with “Driving Assistant Plus”
  • A 2017 Mercedes-Benz E-Class with “Drive Pilot”
  • A 2018 Tesla Model 3 and a 2016 Model S with “Autopilot” (software versions 8.1 and 7.1, respectively)
  • A 2018 Volvo S90 with “Pilot Assist”

The systems tested—specifically, adaptive cruise control (ACC) and active lane-keeping—are designated as Level 2 on the Society of Automotive Engineers (SAE) fivel-level scale of autonomy. That means they can assist with steering, speed control, and following distance, but they don’t allow the driver to be fully disengaged from operating the vehicle.

“The new tests are an outgrowth of our research on Level 2 autonomy,” says Jessica Jermakian, IIHS senior research engineer. “We zeroed in on situations our staff has identified as areas of concern during test drives with Level 2 systems, then used that feedback to develop road and track scenarios to compare vehicles.”

Adaptive Cruise Control

On a controlled test track, IIHS put the cars through four tests to evaluate their adaptive-cruise-control systems and find out how well how the systems accelerate and decelerate.

Each vehicle was driven at 31 mph toward a stationary target to test automatic emergency braking with adaptive cruise control off and autobrake turned on. Only the two Teslas failed to stop in time. When the same test was performed with adaptive cruise control on, all cars were able to avoid the target The 5-series, E-Class, Tesla Model 3, and Tesla Model S were able to brake earlier and gentler than the Volvo S90 while still avoiding the target.

When the test vehicles followed a car that changed lanes, revealing a stopped vehicle, researchers noted that the Volvo slowed down more rapidly than the other four vehicles, braking at a forceful 1.1g.

Another scenario involved the test vehicle following a lead vehicle, which then changed lanes to reveal a stationary inflatable target vehicle in the path ahead. None of the vehicles crashed into the target. Yet again, though, according to the IIHS study, results varied significantly from brand to brand; the 5 series, E-Class, and Teslas all were able to earlier and gentler than the Volvo S90, similar to the active ACC test.

Active Lane Keeping

IIHS Engineers focused on two situations that challenge active lane-keeping systems—negotiating curves and hills—in tests on open roads with no other vehicles around. They also observed how the systems performed in traffic. Lane-keeping assist systems have the potential to save 8,000 lives per year, according to IIHS, while lane-departure warning systems have been credited with an 11% drop in sideswipe and head-on collisions, as well as a 21% reduction in injury rates for those accidents.

All five systems provide steering assistance that centers the vehicle within clearly marked lanes. They also may use a lead vehicle as a guide when traveling at lower speeds or when the lead vehicle is blocking the system’s view of the lane markers ahead.

The Tesla Model 3 performed well in on-road, active lane-keeping tests. (Source: IIHS)

Among the five vehicles, only the Tesla Model 3 stayed in its lane during all tests, while the Tesla Model S overcorrected during one run that caused it to cross the inside line of the turn. The Mercedes-Benz E-Class stayed in its lane nine out of 17 times, disengaging during one run and crossing the inside line twice. The Volvo S90 crossed the inside lane eight times. And the BMW 5 Series stayed in its lane in only three of the 16 runs and was observed to be the most likely to disengage.

Three vehicles, the Tesla Model S, Volvo S90, and BMW 5 Series, came up short when hills were involved, with the 5 Series showing a tendency to steer toward or across the lane line and failing to stay in its lane in all 14 of the hill trials. Tesla’s Model S was only slightly better, staying in its lane in five of the 18 trials with a tendency to swerve left and right when going uphill before finding the correct place in its lane. The Volvo S90 stayed in its lane for nine of the 16 trials—the car crossed the lane line twice and disengaged steering assistance four times when cresting hills.

One issue that test drivers noted among some of the vehicles was a propensity to follow a lead vehicle into the exit lane in slow-moving traffic, even though the driver intended to stay the course. When a car is traveling too slow to track lane lines, active lane-keeping systems use the vehicle in front as a guide. If the lead vehicle exits, the trailing car might, too.

Taking all of the tests together, IIHS concluded that they “can’t say yet which company has the safest implementation of Level 2 driver assistance,” but that it was “important to note that none of these vehicles are capable of driving safely on their own.”

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