|Former U.S. President Barack Obama driving a car. / Photo by: Peter J. Souza via Wikimedia Commons|
The Insurance Institute for Highway Safety (IIHS) recently published on its website a report on its evaluation of adaptive cruise control (ACC) that revealed an issue in self-driving cars when slowing down or stopping for obstacles. IIHS engineers found that current ACC systems have varying performances in typical driving conditions.
ACC is designed to maintain a car's specific speed and following distance from the vehicle in front. The system slows the car down when there are other vehicles ahead, and even initiates full-stop if needed. However, it may not react to vehicles that are already in full-stop.
To find out why autonomous cars fail to stop so it won't crash into a stationary obstacle, the engineers evaluated the ACCs of different smart cars--2017 BMW 5-series with Driving Assistant Plus, 2017 Mercedes Benz E-Class with Drive Pilot, Tesla's 2018 Model 3 and 2016 Model S with Autopilot--in four different track tests.
In the first test, the team tested auto-brake performance by driving the cars at 31 mph toward a non-moving vehicle with ACC disabled. Only the Tesla cars hit the vehicle. In the second test with both ACC and auto-brake on, all of the cars braked earlier yet gentler than an emergency brake.
In the third test, the cars were following a lead vehicle that slowed down to a stop and then accelerated. The engineers found that all cars reduced their speed smoothly. The fourth test, which involved the sudden lane shift of the lead vehicle that revealed a stationary vehicle ahead, leaving the test cars only 4.3 seconds to react before a collision, none of them hit the stationary vehicle. Overall, these tests showed good performance in a controlled environment.
But when the engineers took the test vehicles to the outside world, they noticed something. The ACC in Model 3 acted overcautiously and slowed down 12 times in a 180-mile drive, seven instances of which were due to tree shadows on the road. The other five times were caused by oncoming vehicles from another lane or cars crossing the road from far ahead.
"The braking events we observed didn't create unsafe conditions because the decelerations were mild and short enough that the vehicle didn't slow too much. However, unnecessary braking could pose crash risks in heavy traffic, especially if it's more forceful," said Jessica Jermakian, a senior research engineer at IIHS.