Advanced driver assistance systems—also known as ADAS—come in a few variations. Blind spot monitoring, collision warnings, and emergency braking act like a second pair of eyes and ears, monitoring the car's environment to warn the driver, or possibly intervene, if a crash looks imminent. Other systems are better thought of as convenience features—things like adaptive cruise control and lane keeping, which relieve some of the burden of driving.
Among the newer of these is the traffic jam assist. It's a variant of adaptive cruise plus lane keeping designed for low-speed stop-start driving on limited-access highways, usually cutting out around 40 mph. But we're still talking about a so-called "level 2" system, where the human driver is responsible for maintaining situational awareness; even more advanced "level 3" assists exist—these allow the driver to completely disengage from the task—but are not the topic for today.
AAA recently put five (unnamed) ADAS systems to the test in the Los Angeles area, blessed as it is with dependable heavy freeway traffic. The testers went out together in morning and afternoon weekday traffic, covering the same routes simultaneously. The vehicles were driven an average of 342 miles (550 km) over 16.2 hours, with the ADAS operated according to each vehicle's user manual. And the cars were instrumented with cameras and GPS to record traffic conditions, behavior, and so on.
In addition to comparing how these ADAS worked in the real world, AAA wanted to compare the performance of some more capable systems that allow drivers to take their hands off the wheel, versus systems that require drivers to keep their hands on.
On average, such systems buy the driver less than 10 minutes of peace in a traffic jam. AAA found that "notable events" were recorded by the data capture systems every 3.2 miles, or 9.1 minutes, on average. And 85 percent of those notable events required the driver to intervene.
As most people who have used adaptive cruise control in traffic can no doubt appreciate, the most common event that required intervention was a car ahead cutting into the driver's lane. These occurred about once every 8.6 miles, or 24.4 minutes, with 90 percent requiring intervention by the driver.
Inadequate lane centering was the next most common event, occurring once every 11.3 miles or 32.2 minutes. Seventy-two percent of those events also required intervention. Not resuming after coming to a halt happened 71 times, each of which required the driver to act. On 57 occasions, the lane keeping or adaptive cruise control deactivated, and there were 43 instances of a test car failing to adequately slow down, of which 70 percent required the driver to hit the brakes.
Hands-on versus hands-off
AAA found that the less-advanced systems that required a driver to keep their hands on the steering wheel experienced notable events at three times the frequency of hands-free systems. Hands-off systems only required intervention every 7.2 miles or 20.1 minutes, whereas the less advanced systems required intervention on average every 2.3 miles or 6.7 minutes. AAA also noted that the hands-off systems told the driver to put their hands back on the wheel every 5.5 miles (or 15.3 minutes) on average.
AAA has some recommendations based on its findings, which could also be categorized under common sense. When you're behind the wheel of a vehicle, you should always remain alert, and AAA cautions that ADAS is "never a substitute for an engaged driver." Don't be distracted, especially by your smartphone. Read the car's user manual and understand how, when, and where its systems can be expected to work. And set an appropriate following distance to the car ahead, even if it means more cut-ins.
The organization says it will encourage automakers to improve ADAS performance, especially cut-in response and lane-centering.
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