Advanced driver assistance systems explained

The purpose of ADAS

ADAS are designed either:

1. to keep drivers from making potentially deadly errors, such as moving into a lane occupied by another vehicle, or
2. to minimize the effects of a mistake they’ve already made, such as tailgating and potentially crashing into the car in front of them.
   

The clear purpose of the most important ADAS features, such as automatic emergency braking (AEB), is to improve safety. Others, such as rain-sensing wipers or traffic-sign recognition, have a “convenience” component. Virtually all ADAS features can be overridden or turned off by the driver.

ADAS first appeared on luxury cars, but basic ADAS features are now standard equipment on virtually all vehicles, regardless of brand, price, or trim level. As of late 2021, at least 1 ADAS feature—usually some form of AEB—was standard or available equipment on about 95% of new cars and light trucks for sale in the U.S. Some automakers (notably Acura, Ford, Honda, Lexus, Subaru, Tesla, Toyota, and Volvo) include multiple ADAS features as standard equipment throughout most of their lineups.

Other automakers—GM and Stellantis (formerly Fiat Chrysler Automobiles), for example—have lagged, although they’ve been catching up in the past year. ADAS are often optional or unavailable on some vehicles, such as limited-run sports cars and, oddly, pickup trucks.

In some instances, the absence or optional nature of ADAS features can be surprising. Although Toyota Safety Sense offers a robust suite of advanced safety features, for example, blind-spot warning—an especially useful feature—remains optional on many Toyota products.

A problem with terminology

An ongoing problem, however, concerns the ADAS terminology used by automakers. This problem takes 2 forms:

1. Various manufacturers use different names to describe the same feature (automatic emergency braking and pre-collision system, for example), which can create confusion for car buyers.
   
2. More dangerous is the practice of using a term that inaccurately describes an ADAS feature’s capabilities, such as full self-driving capability. In that example, a AAA survey indicated that upon hearing this term, 40% of respondents erroneously believed that such a vehicle could drive itself. The takeaway: Misunderstanding the capability of a vehicle’s advanced safety features can have deadly consequences.

Basic ADAS features

There’s no such thing as a “standard” set of ADAS features that all automakers offer. That said, the following list represents the ADAS features commonly found on today’s vehicles—a “core” set of advanced safety features, if you will.

These features help prevent or mitigate some of the most serious kinds of collisions and dangerous driving situations, such as rear-ending or sideswiping another vehicle or falling asleep at the wheel. If you’re buying a new (or used) car, it’s smart to get as many of these features on it as you can.

1. Forward-collision warning

FCW uses illuminated symbols on the instrument panel, sounds, or vibration to let a driver know of an imminent crash with a car, person, animal, or other object in front of it—but it doesn’t apply the brakes to prevent the crash.

AAA tested FCW systems by driving vehicles at varying speeds toward obstructions on a test track. Some FCW systems didn’t consistently recognize the obstacles or warn drivers, so it’s important for people who own automobiles with FCW to understand their system’s limitations. The Insurance Institute for Highway Safety (IIHS), a safety organization underwritten by the insurance industry, estimates that FCW reduces front-to-rear crashes by 27% and front-to-rear crashes with injuries by 20%.

2. Automatic emergency braking

AEB is similar to FCW in that it warns drivers of a possible collision with the car in front of them; the big difference is that if they don’t respond, it applies the vehicle’s brakes. Some AEB systems stop a vehicle completely; others merely slow it down. Some automakers make a distinction based on the speed at which the systems operate: city automatic emergency braking (CAEB) or highway automatic emergency braking (HAEB).

AEB is a highly important safety feature because about 25% of car crashes involve a rear-end collision, resulting in almost 2,000 deaths and a half million injuries per year in the U.S. In its testing, AAA found that AEB systems generally work as designed. An IIHS study of AEB-equipped vehicles found that they were involved in 50% fewer front-to-rear crashes and 56% fewer front-to-rear crashes with injuries. A University of Michigan Transportation Research Institute (UMTRI) study found that vehicles equipped with both AEB and FCW were involved in 46% fewer front-to-rear crashes.

But not all AEB systems work in the same way, and they’re not foolproof. They can temporarily malfunction if, say, the sun shines directly into a windshield-mounted camera. If your vehicle has AEB, read your owner’s manual to understand how the system works.

An increasing number of AEB systems are designed to detect pedestrians and bicyclists, which is particularly important because pedestrian deaths have been on the rise in recent years. Unfortunately, AAA’s testing has shown that current pedestrian-detection systems are, for the most part, only minimally effective.

3. Adaptive cruise control

ACC uses cameras, lasers, and radar to control a vehicle’s acceleration and braking. The driver sets an initial speed and distance, and ACC continuously adjusts the vehicle’s speed so that the car keeps a safe distance from the one in front of it. Some ACC systems can anticipate curves or read speed-limit signs and slow the car accordingly. AAA has tested a variety of ACC systems and concluded that, in general, they did a good job of maintaining a specified following distance behind slower-moving vehicles on a highway.

4. Blind-spot warning

BSW alerts drivers to cars in lanes adjacent to their vehicle that they might not see. In those circumstances, a small icon, typically in the side-view mirrors, lights up to indicate that it’s unsafe to make a lane change. The BSW systems in some cars display a camera view of any vehicles in the blind spots on the center touch screen. Ford and Ram have developed BSW systems for their pickups that detect blind spots all the way to the back of an attached trailer.

If drivers activate a turn signal when a vehicle is in their blind spot, the symbol in the mirror flashes and sometimes a warning tone sounds to caution against the lane change. The best BSW systems have an extended range and provide mild steering and/or braking input to prevent possible side-swipe collisions.

AAA staff drove vehicles at varying speeds on an oval track to evaluate their ability to detect a vehicle or motorcycle in their blind spots. Under most—but not all—conditions, BSW systems detected the target vehicles. On average, however, they detected motorcycles 26% later than other types of vehicles.

IIHS research concluded that BSW reduced lane-change crashes by 14% and lane-change injury crashes by 23%. A study by UMTRI found that BSW reduced lane-change crashes by 26%.

If all vehicles were equipped with BSW, IIHS estimates that about 50,000 crashes a year could be prevented. Given BSW’s usefulness, it’s unfortunate that it’s an extra-cost feature on many vehicles rather than standard equipment.

Despite BSW’s effectiveness, AAA recommends that drivers not become overly reliant on it. Instead, they should look in a side mirror, and if they see a lit symbol, they’ll know it’s not safe to make a lane change. If they don’t see a symbol, they should check the mirror carefully anyway, because a car might be moving up quickly beside them or might not have entered their vehicle’s detection zone.

5. Rear cross-traffic warning

RCTW assists drivers who are traveling in reverse (backing out of a parking space, for example) by detecting vehicles, bicycles, or people approaching from the rear or the side. RCTW can detect objects from a larger area than can be seen by a rearview camera alone.

RCTW systems usually flash a warning signal in the side mirror or in a rearview-camera display on the center touch screen. RCTW is typically paired with BSW because both systems rely on radar or ultrasonic sensors in a vehicle’s rear bumper or quarter panels.

AAA evaluated several RCTW systems to see whether they detected motorcycles, bicycles, and pedestrians, in addition to cars. Some systems performed well, but others either missed obstacles or were slow to detect them. When large SUVs were parked on either side of a test vehicle, for example, 2 of the 5 test vehicles weren’t able to detect cars coming from behind. Only 2 of the 5 systems detected a pedestrian crossing behind, and just 3 in 5 detected a bicycle.

AAA recommends that motorists not rely too heavily on RCTW systems and be aware of their limitations. Before backing up, drivers should look to the right and left, over their shoulders, and check out the side mirrors and center touch screen. A UMTRI study found that RCTW reduced backing collisions by 52%.

6. Reverse automatic emergency braking

RAEB enhances RCTW in an important way. When RCTW detects vehicles, pedestrians, cyclists, or other objects, the feature applies a vehicle’s brakes if the driver doesn’t, preventing a collision or reducing its impact. IIHS estimates that RCTW and RAEB combined reduce backing crashes by 78%. A UMTRI study found that RAEB reduced backing crashes by 81%.

7. Lane-departure warning

LDW uses a front-mounted camera that detects painted lines and raised pavement markers to help drivers stay in their lanes. If a vehicle starts drifting out of its lane, LDW alerts the driver with a beeping sound, a flashing icon, a vibration in the steering wheel or driver’s seat, or some combination of all 3. Drivers can override the corrections by turning their vehicle back into its lane.

LDW doesn’t function when a driver activates a turn signal because it assumes, probably correctly, that the driver wants to change lanes. LDW and lane-keeping assistance (described next) can help prevent side-swipe collisions, which account for about 1.5 million crashes each year. IIHS estimates that LDW reduces side-swipe crashes by 11% and side-swipe crashes with injuries by 21%.

8. Lane-keeping assistance

LKA takes LDW a step further. It detects when a vehicle is drifting out of its lane and guides it back. However, if your car has LKA, that doesn’t mean the car can steer itself. LKA systems typically alert drivers to regrip the wheel if they’ve driven hands-free for more than about 10 seconds.

9. Lane-centering assistance

Newer ADAS features

In general, consumers like advanced safety systems, and automakers have developed more than a dozen new safety features in the past few years. Some are variations on or refinements of existing features; others are completely new. We’ll mention a few of the most notable ones.