I was always taught that the mechanical override was shifting it out of drive and into neutral.
Yes, it's unnerving.
Once the clutch plates are no longer in contact the engine can do whatever it wants but none of that makes it to the wheels. And then you can get the car out of gear to coast, turn the whole car off and then back on.
There's no substitute to having a human being in the loop to execute high-level "executive" functions, especially when things aren't done to the very high standards of aerospace. You know, like cars.
There exist "manual transmission" that lack an operator controlled clutch. DCTs are very much manual transmissions, but many of them rely on a TCM to disengage the clutches.
There are all sorts of advanced DSG / dual-clutched transmissions in many newer cars, but even some older cars like the MR2 and Smart cars have a http://en.wikipedia.org/wiki/Electrohydraulic_manual_transmi... : quite literally a manual transmission where the clutch has been actuated electronically.
If you have computer-assisted hill starts, collision avoidance, or computer assisted braking [through ABS, certain traction & stability control systems, etc] your computer has control of your brakes.
If you have range-assisted cruise control, or early collision alert, your computer likely has total control over your throttle.
If you have parking assist, lane departure warning, lane following assist, or electric power steering etc: your computer has control over your steering.
If your car has a DCT: your computer has control over your shifting _as well as both clutches._ -- Meaning you have _no mechanical interface_ to disengage the motor from the transmission. This is similar to your Prius example: the shifter is not mechanical.
On many new cars: there's no ignition key to remove. You likely have a smart "keyfob" that simply needs to be within X-feet of the car, and then you have a push button ignition.
I'm sure there's some override for the button [push and hold for three seconds], but it's still going to go through some electronics to figure that out.
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The only bit that scares me is that all these systems potentially share the CAN bus with the horrendous "Infotainment" systems that every manufacturer loves to install. shudders
I have to admit though I'm surprised that some of those accessories even require a bus as they're typically operated by simple switches.
I guess door locks, wipers, etc. make some sense: with the prevalence of central locking, as well as wipers that sense rain and things like that.
Windows are a bit odd, as they just need a very simple switch. I suppose having all the accessories on a common bus must simplify the wiring harness though.
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I'm curious how TESLA integrates their in-dash system with the rest of the car.
I thought their in-dash console could control some rather safety-critical "preferences" of the car ... for instance I thought you could adjust the level of regenerative braking.
(Other manufacturers are also offering "sport modes", etc -- though they're not always controllable through the dash.)
They certainly don't require a bus in principle. However, if you want to understand both the business case and some very good engineering reasoning behind the use of data buses to control simple automobile accessories you should have a look at the wiring harness for an early 90's Mercedes or similar luxury car. Demand for fancy features drove the number of wires running to and fro to an unmanageable level. Having a mile of wires in a car is expensive for many reasons I'm sure you can imagine, as well as each connection point becoming an opportunity for something to go wrong.
I'm also curious how electric cars in general will manage safety systems going forward, especially in light of this Toyota court decision.
The explanation always seemed obvious to me: Non-technical driver experiences UA. In a panic shifts into neutral. Hears engine scream. Thinks, "The car is still going!" and doesn't realize that despite the sound, the car is actually slowing down.
I know this to be a common misconception in my experience. People commonly misinterpret high revs with "going fast".
But I had not considered that this correlation is only intuitive to me because I own a car with a manual transmission.
But then, people can react irrationally (or not at all) in a full on panic.