[buro9]

I have a Volvo S90 and use both the adaptive cruise control and the steering assist ("Pilot assist" in their language).

Adaptive cruise control I mostly trust. It keeps a set distance behind a car, and that distance varies with speed (think of it as safe braking distance, faster requires more distance).

The only gotcha with adaptive cruise control is if you navigate junctions with it on, i.e. a mini-roundabout on a UK road may be a "straight on" thing and you might see that no-one is going to cross your path, but if you're fixed to a vehicle in front and it happens to turn, then your car will have slowed as it slowed, and then once it detects the obstacle is not there your car will accelerate back to the top speed set in the cruise control. In the UK this could mean going from 20mph to 60mph on a rural road which is a hell of a change.

Steering assist I barely trust. It watches the white lines and seems to favour one side of the vehicle. For clearly and consistently marked lanes of adequate width on only gently curving roads, where you are travelling between 20mph and 70mph, everything is fine.

The gotcha with steering assist is the lack of quality in road surfaces, visibility of lines, missing lane markers, narrow lanes. In these situations the car will have centred me off-centre and I risk being in the oncoming lane on rural roads, or a bend is too dramatic and the car sounds an alarm to get control.

In both cases I do not consider the car as driving itself, I accept these are convenience controls that are limited and so I remain very engaged. Adaptive cruise control is 90% trust worthy but I am wary at lower speeds and small junctions. Steering assist I use only on motorways and dual carriageways now, and never in the slow lane (where motorway ramps, merges, and splits may affect line markings).

One would be wise to not consider the vehicle as being smart.

Scariest moment I've had was actually a different system... collision avoidance.

Edit: There's also an always-on "lane keeping" system which is like the steering assist except it feels like resistance on the steering wheel if you drift over lane markings without having indicated that you intended to. This system I do like.

[sandworm101]

>>Adaptive cruise control I mostly trust. It keeps a set distance behind a car,

Sounds like you are also trusting that car. Would this system follow a car into a dangerous situation? I ran into this sometimes while riding sportbikes. Some car would be following us on a strait, a passing lane, but come the first turn it was way out of its league. I saw more than a couple sliding sideways in my mirror.

This doesn't have to involve speeding. On a mountain highway (BC) fast straits often end in very tight corners. The speed limit doesn't change. Braking, merging and cornering all have to happen simultaneously. Leading bikes in a group will sometimes even accelerate into corners to create space for those behind to maneuver. Any car setting its speed according to the bikes ahead of it is in for a nasty surprise.

[stephengillie]

> Sounds like you are also trusting that car. Would this system follow a car into a dangerous situation?

This is more true than it can seem at first. For the GP's point, adaptive cruise behind a car slowing to turn can cause unexpected braking and startle drivers.

Adaptive cruise around sharp corners exposes the current limits of self-driving car vision. These systems usually have a cone of vision in front of the car, that only sees stuff moving 25+ mph in the same direction. Once a leading car is too far around a curve, the adaptive cruise can lose track of the leading car and accelerate sharply.

Some adaptive cruise systems intentionally don't accelerate while on curves, likely for this reason.

[magduf]

Something like this happened to me not long ago, but in my car (a good-handling economy car (Mazda)): some asshole in a big Mercedes SUV was tailgating me very closely, pissed that I wasn't going fast enough for him, and he was unable to get around me on this long exit lane. Well the single lane then turned into a ramp, which I took at a pretty fast speed (for a car), as I usually do, and he almost wrecked because his vehicle couldn't handle the turn.

Later, when I was pulling into a left-turn lane and thought he was gone on his way, this asshole intentionally cut right in front of me.

[alexhutcheson]

I wouldn’t use the adaptive cruise control on a mountain highway, or any other setting with possibly sharp turns where I have to adjust speed up and down. I wouldn’t use normal cruise control in that setting either.

[sandworm101]

But my point still stands. If you are letting the machine set your speed according to the car ahead, what if that car's speed is not appropriate for you? Does the machine make a judgement as to the performance abilities of the car ahead? Humans wouldn't follow as close to a Porsche as they would a truck. You don't want to be too close to something that can stop far faster than you can.

If the adaptive cruise control is staying far enough away that it can always stop that is an entirely different problem. Leaving so much distance, so much empty road, between cars reduces the total carrying capacity of the lane, which isn't good for anyone.