What are active safety features and how do they work?

Rear Cross Traffic Alert is{ } included in Nissan Safety Shield 360. (Image courtesy of Nissan North America)

Safety has always been a top concern for car shoppers. Recently, it has become a source of frustration.

Nearly a quarter of car shoppers who bought or leased a model year 2019 vehicle found the technology to be annoying or bothersome, according to a J.D. Power study of more than 20,000 consumers within the first 90 days of ownership. Many of the annoyed, and those who weren’t, disabled the systems. These results are consistent with an IIHS study from 2017.

Part of the annoyance is confusion. Shoppers aren’t sure what they’re getting, how it works, and what it’ll do once it works. Chances are they get used to it after awhile, or don’t appreciate its value until it prevents a crash.

Whatever the case, it’s confusing. As shoppers continue to use these features, and automakers such as Toyota, Honda, Nissan, Volvo, and others (but not the Big Three in Detroit) offer active safety features as standard equipment across product lines, we want to clear up the confusion.

We’re going to adhere to the naming conventions first put forth by the National Safety Council, who are one of nearly a dozen organizations such as Consumer Reports, AAA and IIHS advocating for singular, streamlined names of the six key active safety features across all automakers (in bold below).

As we accept Level 2 semi-autonomous driving as the new reality, we hope all automakers will adopt these naming conventions so consumers will actually know what their cars can and cannot do. Keep in mind, there is no such thing yet as a self-driving production vehicle, which happens in Level 4 autonomy. Here's a primer on the levels of autonomy.

For now and the foreseeable future, we’ll have the following safety features to mitigate or prevent crashes.


FCW: Forward collision warning can beep, buzz, or flash “BRAKE!” in the instrument cluster if it detects an impending collision with a forward object, such as a car stopped or slowing in a lane. Camera- or radar-based sensors in the front bumper or mounted up by the rearview mirror are responsible for the detecting. Aggressive drivers who are active lane changers may not appreciate the more sensitive systems that sound alarms when an aggressive driver might not feel alarmed.

PD: Pedestrian detection is usually used in concert with FCW. It can detect moving animate objects.

AEB: Automatic emergency braking uses sensors to detect a stopped or slowing vehicle and automatically brake the car quicker than the driver can. It can be broken down into high speed (HAEB) or low speed (CAEB), with the C designating City. The best systems can also detect pedestrians and cyclists. Audible, visual, and even haptic alerts usually accompany the system's activation, which works in the same way as FCW but will actually apply the brakes. The same technology enables adaptive cruise control. It is considered one of the most important safety advancements since electronic stability control, which was mandated for model year 2012 vehicles and has been considered the most important safety advancement since the safety belt. All major automakers voluntarily agreed to make AEB standard for model year 2022 vehicles.

AH: Adaptive headlights follow the road, or move side to side with the steering wheel. It projects light on the direction the car is going, to shed more light on what is coming. Sensors that detect steering wheel angle swivel the lights in that direction.

HBA: High-beam assist automatically turns on and off the brights when it is too dark and also when it detects oncoming traffic. Sometimes it can put on the brights when the driver might not normally. Sensors, often mounted in the rearview mirror, detects both oncoming headlights or lead taillights, to turn the lights back to normal. When the darkened road is clear, the high-beams come back on.


LDW: Lane departure warning issues a beep or flashes a light or vibrates the seat when the car drifts out of its lane. The camera-based system on clear lane markings, so snow or other debris will confuse it. Using the indicator will disable it for the moment.

LKA: Lane keeping assist can provide hands free driving for a set amount of time, often 20 seconds or so, as long as the camera-based sensors can read road lines or sense neighboring vehicles. It can torque the steering wheel if you don’t put on an indicator when changing lanes. It can also brake the vehicle if changing lanes when it detects a neighboring vehicle.

ALC/LCA: Active lane control, which is the nomenclature we advocate for instead of lane-centering assist, encompasses lane keeping assist but represents an evolution of it into Level 3 autonomy. Using cameras and sensors, it keeps the vehicle centered in the lane but for an unlimited amount of hands-free time. The 2020 BMW X7 can do it under 37 mph, Cadillac Super Cruise uses radar on the outside and a camera-based sensor on the inside to make sure the driver's head and eyes are still on the road, and Tesla's misnomered AutoPilot reads lane markings and vehicles.

Sure, when it comes to our insistence on "active lane control," it appears our hypocrisy knows no bounds, like Doc Holiday says in "Tombstone," but we feel strongly that "active lane control" is much more distinct and less confusing than lane-centering assist.

BSW: Blind spot warning alerts with audible, visual, or haptic warnings when a car or sometimes bike is coming up in your blindspot. The best systems flash a small but noticeable warning icon in the side mirrors. If you use an indicator, and for the love of cars, please use a turn signal when changing lanes, an additional alarm can sound. The sensors are usually located in the rear or side rear of the vehicle.

BD: Bicycle detection is excellent for urban drivers. Like PD, it can detect bicycles crossing in front of the vehicle. Honda’s LaneWatch takes it a step further, with a camera mounted backward on the passenger side mirror. If you turn on your right indicator, it projects moving objects like cyclists coming up on your blindspot onto the rearview camera screen. Unfortunately, Honda is dropping LaneWatch on new models in favor of more sophisticated BSW.


RCTA: Rear cross-traffic alert detects traffic crossing behind the vehicle when it’s in reverse. So if you’re parallel parking it shouldn’t go off, but if you’re backing out of a driveway or parking spot and car is coming from either side, it will beep or buzz or vibrate. Sensors are typically located in the rear bumper.

Rear AEB: Same thing as AEB except when the car is in reverse, and the sensors are located in the rear of the vehicle. It can stop the vehicle based on rear cross traffic alerts or if it detects a stationary object, like a kid’s bike left in the driveway.

All of these sensors and systems enable semi-autonomous driving features, such as adaptive cruise control (ACC), which regulates speed based on the cars in front of you, so you don’t have to hit resume or cancel on the cruise, just set the desired proximity from the lead car and the system takes over. The best go down to a stop and restart for bumper to bumper traffic. The worst of them leave a gap big enough between you and the lead car to fit two or three semis.