[SystemSafety] Yet another supposedly-runaway car

[michael.ellims at tesco.net]

Peter wrote: And why is it happening now, and not (say) twenty years ago?

It was happening 20 years ago, there are numerous cases of mechanical faults that would cause the throttle to jam open at the last operating point. One very common cause was the throttle cable becoming jammed. More recently, and with an electronic throttle there was a recall due to the throttle plate becoming jammed in the throttle body. Further back than that a common cause was the floor of the vehicle rusting out and the pedal falling though the floor or otherwise becoming jammed which is the reason that in more recent vehicles the pedal arm is suspended rather than floor mounted. Been there, had that, it took about 10 minutes to sort out

Peter wrote: Are they due, perhaps, to people becoming "frozen"?

The last two cases in England where this occurred in both cases the drivers were both prosecuted successfully for dangerous driving. In one case it was the second time that the driver had been caught by police in a “runaway” vehicle. That driver was driving a BMW with a mechanical throttle as well and no mechanical faults were found. It’s notable that in both cases the runaway occurred after the police tried to stop them for exceeding the speed limit.

A similar case occurred in Australia about four years ago and I spend half a day working though the wiring diagrams for the vehicle concerned. In that case the the ignition switch was connected to both the engine ECU and to a replay for the fuel pump. Again in that case as the driver claimed that the brakes wouldn’t slow the vehicle, that he couldn’t put it into neutral and he couldn’t turn it off.

Nancy wrote: > This particular case is a little suspect although I don't doubt most of them.

If you do look at the video it’s stated that the chase reached speeds of 100 (or 120) mph – however the distance covered is stated as 113 miles in ninety minutes which gives an average speed of only 75 mph. There is probably some variation due to topography but from Dallas to Sulphur Springs the elevation difference is only around 50-100 feet. Looking at the police camera information it’s not clear if speed is displayed.

I’ve checked the NHTSA database and there doesn’t seem to be an investigation on the vehicle type active thought there is one for stuck throttles on the Ford Taurus (PE12-033) and Accelerator Pedal Interference (EA12-009). There is also a complaint (but no investigation) about the floor mats interfering with the throttle pedal on the vehicle concerned.

Peter wrote: “turn off the ignition" or "force it out of gear / force the automatic-shift lever into "Park".

NEVER put a moving vehicle with an automatic transmission into Park!!!! This will lock the rear wheels as P engages the transmission lock. At speed this will result in the vehicle spinning. This is also probably impossible as you would have to go though Reverse to get there which would do the same thing – the gearshift is called a PRNDL for a reason ;-)

You should be able to get most automatic gearboxes into neutral though it may not be possible an electronically controlled one. However it may not be easy , personally I don’t know because I try to not drive automatics – no clutch.

One significant problem here is that beyond what drivers normally do (i.e. brake or steer) there are possibly very few actions they will take effectively. For example if it is difficult to shift from drive to neutral then a driver might try it, find it hard, and not complete the action. Likewise with a push button ignition you may have to hold it down for an extended period e.g. 5 seconds on a Lexus. This is a very long time in an emergency situation and again there is a  high probability that it will be performed incompletely.

Note that NHTSA consider this last issue a significant human factors problem and are in the process of rulemaking to mandate that the time be the same for stationary and moving vehicles which should make it more “natural” thing to do (BTW I like ignition keys).

I’ve included references to a couple of freely available papers that may be of interest (sorry one is mine) a search in Google Scholar finds both.

Dilich, M., Kopernik, D., and Goebelbecker, J., "Evaluating Driver Response to a Sudden Emergency: Issues of Expectancy, Emotional Arousal and Uncertainty," SAE Technical Paper 2002-01-0089, 2002.

M. Ellims, H. Monkhouse , Agonising over ASILS: Controllability and the In-Wheel Motor, The 7th IET International System Safety Conference 2012, Edinburgh UK.

Paradoxically this possibly means that the worst drivers  (e.g. boy racers) are the ones best able to cope with an emergency situation - because they have practiced being in situations that resemble them all the time.


Dr Michael Ellims
Systems Safety Consultant