Buried in a recent issue of my newspaper the other day, squashed into a corner between an advert for luxury cruise holidays and a delightful close-up photo of some newly-discovered bacterium, was a short item about a recall by a major UK-based motor manufacturer. It said that in some circumstances the cruise control of some of its diesel models, if engaged, cannot be disengaged in the "normal manner".
The article went on to explain the company had contacted drivers and warned them that "in some circumstances the cruise control may not respond to the normal inputs". I looked in the handbook for my car and the "normal inputs" for turning off the cruise control are the switch on the steering column and hitting the brakes in panic. In most cases, I suspect that the latter of these is the most useful one, but it would certainly be nice to know that at least one of them worked.
However there's no need for concern because, as the company explained, turning the ignition off cancels the cruise control function. Of course, it also turns off the power assistance to both braking and steering functions. Try it sometime (preferably at no more than five miles per hour) - you need arms like a gorilla and feet like an elephant to make them work.
So it seems further scrutiny of the short article suggests that the sequence of events following the solution may be somewhat more complex than originally suggested in the rather optimistic euphemisms provided. As a regular reader you will, of course, realize that here at p&p we are resolutely scenario-focused, and so our guidance on recommended actions would be much more useful. We'd say something like this:
Scenario: You are traveling on a main road at 70 miles per hour and encounter a roundabout.
Problem: You anticipate that entering the roundabout at 70 miles per hour may not be conducive with safe driving techniques, may impact the stability of the vehicle, and the centrifugal force generated is likely to exceed the tyres' capacity for grip on the road surface.
Actions: Apply force to the brake pedal. Panic when nothing happens (optional). Turn off the cruise control using the switch on the steering column. Panic when nothing happens (less optional).
Forces: The engine will continue to run at speed even when you apply normal inputs to the cruise control function, impacting your ability to reduce speed. To counter this, consider turning off the ignition.
Liabilities: Turning off the ignition will severely reduce the efficiency and throughput of steering and braking functions.
Solution: You are going to die.
Surely that's a lot more informative and useful? And an obvious justification for our scenario-based approach to user guidance. Maybe they'll give us the job of writing the handbook for their next new model...