Bad interface design or something more?

June 23, 2012 12:33 PM

What is the purpose of the on/off switch on my car's cruise control?

I don't understand why cruise control doesn't just remain always on by default. Is there any reason why I should ever turn mine off?

(In case it isn't clear, I'm talking about the distinction between [on/off] and [set/unset/accel/decel], which are two separate controls. I don't want to drive everywhere with cruise-controlled speed, but can I leave the CC system on even while it's not set?)

posted by The Winsome Parker Lewis to Technology (25 answers total)

I always leave on, with no ill effects. I sometimes use the switch to cancel CC without stepping on the brake; I suppose that saves brake pad wear.
posted by Johnny Wallflower at 12:39 PM on June 23, 2012

You turn it off for city driving. You could keep it on, but if you accidentally hit accel, you might have an accident.
posted by Ruthless Bunny at 12:40 PM on June 23, 2012 [1 favorite]

It's a vestige of UI design transplanted from other gadgets.

Many other cars have been designed by designers who agree with you, and don't have that many cruise-control buttons. I've seen cars with as few as three buttons perform the following combined functions:

button #1: on / set / accel
button #2: decel
button #3: off / unset

Sorry...can't remember which cars.
posted by wutangclan at 12:43 PM on June 23, 2012

It's an additional safety layer, supposed to prevent an accidental use of cruise control in an unwanted situation. I assume it's a required item, because all the cars I have driven with cruise control have had an on/off switch.
posted by Forktine at 12:45 PM on June 23, 2012

Because accidentally bumping the set button could be dangerous. Imaging you are expecting that taking your foot off the gas would cause deceleration, and then it doesn't?

It's easy to think "then I'd just step on the brakes!" However, that's not the actual response of a non trivial portion of drivers. The actual response is freaking the fuck out because the car is broken.

So having two barriers to cruise control is a Good Thing.

Bonus points for the problem of setting it inadvertently, being unfamiliar with the vehicle or unable to look at the wheel. Instead of mashing the break, imagine you're trying to turn the CC off by mashing the button panel. Except you're pressing accelerate. Crash.
posted by bilabial at 12:46 PM on June 23, 2012 [3 favorites]

I seem to remember it being connected to the need to electrically isolate the cruise control system entirely - ie so none of the buttons work (as Forktine suggests).

Every car I have driven has had a full on/off switch. The annoying ones are not a physical switch that you need to reengage the cruise every time you restart the car.
posted by Brockles at 12:48 PM on June 23, 2012 [1 favorite]

Sorry...can't remember which cars.

Oh what am I talking about...I have a very concrete example: my own 2011 3-series (E91) BMW.
posted by wutangclan at 12:49 PM on June 23, 2012

A cruise control system is running software, if it went haywire one day and locked up while you were travelling at speed, I think you'd really want the off switch then.
posted by Lanark at 12:54 PM on June 23, 2012

All the Toyotas I've had in the past 5-6 years have a full on/off switch that defaults to OFF every. time. you. turn. off. the car. All the controls are on a stalk on the right.

I think it is either a US regulation, a switch for the lawyers, or both.

My riding lawnmower also has 2 mechanical steps that must be engaged before you can mow in reverse. Ditto.
posted by randomkeystrike at 1:01 PM on June 23, 2012

Cruise control can kill you if it is raining or icy. I would turn it off in those circumstances. If your wheels are slipping or hydroplaning, cruise control says "accelerate" which increases the wheelspin, which can send you off the road when the wheels grab at 120 mph.
posted by weapons-grade pandemonium at 1:13 PM on June 23, 2012 [1 favorite]

I wonder if it may have something to do with ponding water/hydroplaning & using cruise control could really have bad results.
posted by kellyblah at 1:15 PM on June 23, 2012 [1 favorite]

More here.
posted by weapons-grade pandemonium at 1:16 PM on June 23, 2012 [1 favorite]

My 07 Honda seems to have it on by default.
posted by theora55 at 1:25 PM on June 23, 2012

Response by poster: I think I've gotten some good answers but a lot of you should probably re-read my original question. I'm not talking about driving with the cruise control activated (i.e., "set"), I'm taking about normal city driving with normal pedal-controlled speed where the cruise control system happens to be "on" but isn't controlling anything (i.e., it's not "set").

It sounds like the answer for the question of why the on/off control exists is mainly a legal one. Presumably some federal law mandates that cars work this way; I would be curious to see that law for myself if anybody knows it.

And bilabial's argument remains that some people might not have the sense to disengage CC via brake pedal if they don't realize it's active. I guess auto manufacturers need to keep the lowest common denominator in mind... but hitting the brake to stop a runaway car is so obvious it's almost condescending to suggest people wouldn't do that. No offense intended to bilabial, I presume you're just relaying the thought process of car engineers. If someone wants his car to stop and does anything other than step on the brake, his problems as a driver are a lot bigger than misunderstanding cruise control.

Seems to me that the "on" and "set" functionality should be combined into one control, and likewise "off" and "cancel" should be combined. If Lanark's assertion is correct that [set/unset/accel/decel] is software and [on/off] is hardware, couldn't they be re-engineered with built-in failsafes? Are there any known cases of someone's CC software locking up and requiring the use of a killswitch?
posted by The Winsome Parker Lewis at 1:43 PM on June 23, 2012

I'm not finding the specific cases, but I read stories about this where the drivers said they were too freaked out to hit the brake or put it in neutral. People get dumb when they're stressed.
I've had the accelerate button get stuck in one of my cars and while I don't know how it might accidentally get going, it did give me some peace of mind to be able to turn the whole system off until I got the gunk cleaned out of it.
posted by gally99 at 2:03 PM on June 23, 2012 [1 favorite]

Here's the excerpt on cruise control* from the driver's manual for my BMW.

I think they've come up with a great design that dispenses with the redundant on/off switch. It's practically impossible to activate accidentally -- knocking it up/down/backwards with your knee or hands will deactivate/decelerate the cruise control. Only pushing the stalk forward activates/accelerates.

* (c) BMW AG, fair use, yadda yadda
posted by wutangclan at 3:12 PM on June 23, 2012

BTW my car is Canadian-spec, which is identical to US-spec except with the addition of daytime running lights and metric-unit instrumentation.
posted by wutangclan at 3:16 PM on June 23, 2012

but hitting the brake to stop a runaway car is so obvious it's almost condescending to suggest people wouldn't do that.

You'd also think that anyone that has a stuck throttle pedal would very easily consider the option of turning the ignition on on a runaway car or just selecting neutral. There is a lot to be said for how dumb humans are when they panic.

Seems to me that the "on" and "set" functionality should be combined into one control, and likewise "off" and "cancel" should be combined. If Lanark's assertion is correct that [set/unset/accel/decel] is software and [on/off] is hardware, couldn't they be re-engineered with built-in failsafes?

Well, they have. With a nice on/off switch (from their perspective). There's not much impetus for them to develop anything else - it's just cost with no benefit (to the manufacturer). There's a lot of momentum in design, even if the legislation is no longer necessary, that redesigning stuff costs time, money and development so why bother?
posted by Brockles at 3:26 PM on June 23, 2012 [1 favorite]

I never use CC, so the off button is useful for me since then I don't have to ever even think about it.
posted by unSane at 4:46 PM on June 23, 2012

It sounds like the answer for the question of why the on/off control exists is mainly a legal one...

I read the question. Do you think getting you killed is mainly a legal answer?
You turn it off in inclement weather so you don't forget and activate it intentionally, or activate it by mistake.
It's kinda like throwing the breaker when you do electrical work on your stove, even though you have the switch off.
posted by weapons-grade pandemonium at 4:47 PM on June 23, 2012 [3 favorites]

The on/off switch made sense long ago when cruise controls were unwieldy electromechanical systems. They could and did go haywire. Now a days I can't think of any reason for them to have any buttons except for "set".
posted by chairface at 7:45 PM on June 23, 2012

A lot of the answers (and the question) read to me as if everyone in the world is familiar with and uses cruise control all the time. Some are even upset that the car turns it off automatically when the car goes off. Why would anyone want it off?

Well, I can tell you that I NEVER use cruise control. Don't really know how, am kind of scared by it, none of the cars that I grew up with ever had it so nobody that I ever drove with ever used it. The last time we bought a car (2004) I was intrigued and told my husband that we should put that on the list of features to include, since we drive a lot of 1100 mile trips. He said it was a waste of money and could be dangerous and we would not put it on the list. The car we ended up choosing had it anyway, so we got it. I've used it maybe 3 times on long distance highway trips. Each time, it was a little bit thrilling and little bit scary. It startled me when the car took over and drove itself. Overall I decided I didn't like it and it does feel a little dangerous to me.

So, I want an on/off switch. Because I want it turned off. I don't want to accidentally bump into the control and find myself suddenly being taken for a ride with an invisible driver. It's not because I'm dumb that I would react weirdly in this scenario - it's because I have no freaking idea what just happened and OMG what is going on here???
posted by CathyG at 7:42 AM on June 24, 2012 [3 favorites]

Here's what I've seen: 80s/early 90s Mercedes-Benz (specifically an 84, 88, and 94), no on-off switch, just the directional stalk similar to modern toyotas, but tiny and without the button on the end.

Early 90s to mid 00s (at least) Honda: mechanical on-off switch on the dash to the left of the wheel that cuts the power to the cruise control system with two buttons on the wheel to handle accel/decel/cancel (press both to cancel, or on newer ones, there is a third small cancel button in between the accel/decel buttons). I like this because the system is always available after the car is started if the switch is left in the on position.

Late 80s through early 00s Ford/Lincoln/Mercury: Five separate buttons on the wheel: On, Off, Accel, Coast, Cancel. Defaults off. (the Lincoln MKS I had as a rental the other day had fewer, but I don't remember the exact configuration)

Modern Toyota: As described earlier, a stalk similar to the MB style, but with an on/off button on the end that annoyingly defaults to off.

I find them all equally usable, although I find the waste of space on the Fords to be a bit annoying. Both Honda and Toyota manage to provide the same hard-off functionality without as much waste. I forget how the GM system works, even though I've had them as rentals for several months of wall clock time.

FWIW, the only time I ever used the on/off switch for the cruise control on the Hondas was when I hadn't figured out that pressing both canceled and didn't want to use the brake to cancel. Thinking back, I suppose I could have just actuated the clutch, since that also canceled cruise on my early 90s model. (as did hitting redline if it popped out of gear unintentionally or otherwise)
posted by wierdo at 9:26 AM on June 24, 2012

No offense intended to bilabial, I presume you're just relaying the thought process of car engineers. If someone wants his car to stop and does anything other than step on the brake, his problems as a driver are a lot bigger than misunderstanding cruise control.

This is, actually, offensive. I apologize for being on my phone and not digging up citations, but this happens. And not just to drivers of cars, but to aircraft pilots. Here's the deal. When something unexpected happens (unexplained acceleration, aircraft turns or dives) the brain in control desperately tries to figure out what went wrong? What is causing this? and puts 'obvious' courses of action so far from mind as to make them practically impossible. "pilot error" in many crashes means "pilot was trying to figure out he cause of the problem instead of landing safely.

Same thing with drivers of cars. Except, a bigger deal because of the far, faaaaar greater number of cars on the road. And the orders of magnitude fewer hours of training we receive in driving them.

So your driver unable to think of the brakes does have a bigger problem. He's about to crash. And this has been studied.
posted by bilabial at 9:33 AM on June 24, 2012 [2 favorites]

Yes, for someone who doesn't ever use CC (eg, brought up and learned to drive in the UK) when a car accelerates faster than you want, your natural response is to take your foot off the gas, not to hit the brake.

If you take your foot off the gas and the car continues to accelerate, you get a 'what the..?' moment. It's not at all obvious at that point that braking will successfully stop the car. What you feel like is that you'll get into a competition between brake and gas and lose control.

The amount of time that it takes to figure out that, yes, you ought to hit the fucking brake is long enough for substantial amount of bad, possibly fatal, stuff to happen.

It's not instinctual.

So thank God for the off switch.
posted by unSane at 9:43 AM on June 24, 2012 [2 favorites]