# Whacko Suggestion for Stopping a Car **URL:** \ **Category:** Factual Questions\ **Created:** [December 15, 1999, 1:51am UTC](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412 "1999-12-15T01:51:00Z")\ **Posts on this page:** 17\ **Page:** 2
**Author:** ![Stephen](https://avatars.discourse-cdn.com/v4/letter/s/96bed5/32.png) [@Stephen](https://boards.straightdope.com/u/Stephen)\ **Post date:** [December 15, 1999, 10:06pm UTC](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412/21 "1999-12-15T22:06:00Z")
> [@](#): > > ## quote: > > ## Further, the required energy in the pulse is going to increase with the distance, at a rate of squares or better. > > is just plain wrong. This is what people learn in high school about energy radiation, and it’s a good place to start. But it applies only to energy radiated spherically. In the case of electromagnetic radiation, there are methods of focusing that can cause the drop in energy to fall off much more slowly than the square of the distance from the source. If you’ve got a cite for true **EMP** that is focusable (not RF jamming, not microwave broadcast, **EMP** ), post it. Otherwise, I’ve got to go with standard amplitude vs. range behavior for electric dipole radiation in the far field (which is how most of the damaging energies propogate in EMP). * * * Stephen [Stephen’s Website](http://stephen.fathom.org) Satellite Hunting 1.1.0 visible satellite pass prediction shareware available for download at [Satellite Hunting](http://stephen.fathom.org/sathunt.html) ---
**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\ **Post date:** [December 15, 1999, 10:31pm UTC](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412/22 "1999-12-15T22:31:00Z")
The delivery by the little car should be interesting for a chase doing a hundred mph, or a snow covered road. ---
**Author:** ![Stephen](https://avatars.discourse-cdn.com/v4/letter/s/96bed5/32.png) [@Stephen](https://boards.straightdope.com/u/Stephen)\ **Post date:** [December 15, 1999, 11:45pm UTC](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412/23 "1999-12-15T23:45:00Z")
> [@](#): > > The problem with an EMP or alternate form of stunning the vehicle is that when all the electronics are fried the power steering becomes inoperative. The driver would invariably loose control of the car. No, the power steering does not become inoperative. Have you ever run out of gas on the freeway? When the power steering pump is no longer running, the steering gets ‘stiff’ and can be very tough to turn through large amounts while moving slowly, but at highway speeds and above, it is hardly a challenge. * * * Stephen [Stephen’s Website](http://stephen.fathom.org) Satellite Hunting 1.1.0 visible satellite pass prediction shareware available for download at [Satellite Hunting](http://stephen.fathom.org/sathunt.html) ---
**Author:** ![Stephen](https://avatars.discourse-cdn.com/v4/letter/s/96bed5/32.png) [@Stephen](https://boards.straightdope.com/u/Stephen)\ **Post date:** [December 16, 1999, 1:09am UTC](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412/24 "1999-12-16T01:09:00Z")
> [@](#): > > So the vehicle is going 90mph & you run this thing on it. What happens when it becomes a 90mph uncontrollable vehicle? > Can you say, ‘missle?’ C’mon people! We’re talking about passenger cars here, not F-16 fly-by-wire fighter jets. An EMP would fry the electronic ignition, stalling the engine and the car would coast to a stop, with somewhat stiffer steering and nothing on the radio. Manny car chases end when the suspect’s tank runs dry and they’re dealing with the same handling characteristics (except they still have radio reception). Also, if someone can provide an actual cite for a **directional** , **EMP** producing device, that doesn’t require an **explosion** , I’ll stop saying that the idea of mounting one on a patrol car is science fiction. * * * Stephen [Stephen’s Website](http://stephen.fathom.org) Satellite Hunting 1.1.0 visible satellite pass prediction shareware available for download at [Satellite Hunting](http://stephen.fathom.org/sathunt.html) ---
**Author:** ![MrKnowItAll](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrknowitall/32/87_2.png) [@MrKnowItAll](https://boards.straightdope.com/u/MrKnowItAll)\ **Post date:** [December 16, 1999, 1:46am UTC](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412/25 "1999-12-16T01:46:00Z")
I agree that the loss of power steering in a high speed chase would hardly be noticable, but what about power brakes? Would they be affected? If so, that could be a huge problem. ---
**Author:** ![Konrad](https://avatars.discourse-cdn.com/v4/letter/k/f475e1/32.png) [@Konrad](https://boards.straightdope.com/u/Konrad)\ **Post date:** [December 16, 1999, 2:06am UTC](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412/26 "1999-12-16T02:06:00Z")
> [@](#): > > when all the electronics are fried the power steering becomes inoperative. The driver would invariably loose control of the car. I’ve been driving my car without power steering for a year now. Frying everthing would be no different than just shutting off the ignition, something I do often while driving. The car will just coast to a stop. Well, a normal car would, mine has hot spots in the engine or something so sometimes when I get out of the car while it’s still moving it will keeping on sputtering along forquite a while. (it’s carbeurated.) It freaks people out sometimes, I’m walking away from the moving car “Aren’t you going to go after it?”, “Nah, it won’t get far.” This is only a problem because my handbrake is broken so I park the car by leaving it in gear. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [December 16, 1999, 2:13am UTC](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412/27 "1999-12-16T02:13:00Z")
OK, so what exactly is EMP? I thought it stands for electromagnetic pulse, i.e. a short burst of electromagnetic radiation. A nuclear blast interacting with the earth’s magnetic field is certainly one way to produce it, but any spark produces a pulse. If my understanding is correct, the only difficulty with focusing EMP is to get a reflector larger than the wavelength of the pulse, but I’d imagine much of the energy is at high frequencies so it’d be no problem. ---
**Author:** ![Stephen](https://avatars.discourse-cdn.com/v4/letter/s/96bed5/32.png) [@Stephen](https://boards.straightdope.com/u/Stephen)\ **Post date:** [December 16, 1999, 2:52am UTC](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412/28 "1999-12-16T02:52:00Z")
> [@](#): > > I agree that the loss of power steering in a high speed chase would hardly be noticable, but what about power brakes? Would they be affected? If so, that could be a huge problem. You have to keep in mind that, when Detroit says “Power” this and “Power” that and they’re talking about a system that affects safety… They mean “Power _Assisted_” People run out of gas on freeways all over the world, every day. If they were careening out of control, with no brakes, regulations would have been passed to correct that. The fact is, the car would act like any stalled car and coast to a stop. The steering would be a little stiffer and the brakes might take a little extra pressure, but no, you won’t have cars suddenly going ballistic (unless the driver is being particularly stupid). > [@](#): > > OK, so what exactly is EMP? I thought it stands for electromagnetic pulse, i.e. a short burst of electromagnetic radiation. A nuclear blast interacting with the earth’s magnetic field is certainly one way to produce it, but any spark produces a pulse. The difference between that spark and an EMP is that the EMP carries with it, several tens of kilovolts per meter, over a frequency range spanning 0.1 to 10 megahertz. It’s a matter of passing a threshold. Air is a pretty decent insulator (that’s why you don’t see wimpy lightening). Just like breaking a noble gas down into an ionizing plasma, you have to pass an energy threshold, before you can have a destructive pulse of electrons passing through open air, car bodies, etc. and frying their electronics from a distance. That threshold is far beyond what would make a practical law enforcement device. > [@](#): > > If my understanding is correct, the only difficulty with focusing EMP is to get a reflector larger than the wavelength of the pulse, but I’d imagine much of the energy is at high frequencies so it’d be no problem. OK, consider you’re building a reflector for a 50 kV/m peak energy in a 200 nanosecond pulse. The bandwith covers 10 kilohertz to 100 megahertz. To complicate things, EMP is a very complex interaction with extremely low frequency effects, such as low frequency current loops in the air. Complex interactions exist between the electrical and magnetic fields, which add a whole layer to questions about directionality (for instance, as mentioned before, in higher geomagnetic latitudes, virtually none of the pulse energy could be directed northward). EMP shielding exists, but it is intended to protect equipment far from the blast, buried underground and **completely** shielded by carefully sealed (perfectly fitted and welded at the seams) sheets of steel. Oh, it has to fit on the front grill of a Crown Victoria and it can’t allow **any** transients to effect the host car. * * * Stephen [Stephen’s Website](http://stephen.fathom.org) Satellite Hunting 1.1.0 visible satellite pass prediction shareware available for download at [Satellite Hunting](http://stephen.fathom.org/sathunt.html) ---
**Author:** ![JoeyBlades](https://avatars.discourse-cdn.com/v4/letter/j/a87d85/32.png) [@JoeyBlades](https://boards.straightdope.com/u/JoeyBlades)\ **Post date:** [December 16, 1999, 1:59pm UTC](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412/29 "1999-12-16T13:59:00Z")
MrKnowItAll asks: > [@](#): > > I agree that the loss of power steering in a high speed chase would hardly be noticable, but what about power brakes? Would they be affected? If so, that could be a huge problem. The power in power brakes comes from hydraulics. If the engine stops the hydraulics will fail, but the brakes still have some basic function. An EMP would knock out the ABS, so your braking would tend to be less controlled. ---
**Author:** ![Stephen](https://avatars.discourse-cdn.com/v4/letter/s/96bed5/32.png) [@Stephen](https://boards.straightdope.com/u/Stephen)\ **Post date:** [December 16, 1999, 3:36pm UTC](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412/30 "1999-12-16T15:36:00Z")
> [@](#): > > An EMP would knock out the ABS, so your braking would tend to be less controlled. But then, only if you tried to lock them up. ABS ‘pulses’ the brakes when you are braking hard enough to cause your tires to slip. ABS does nothing during normal stops. * * * Stephen [Stephen’s Website](http://stephen.fathom.org) Satellite Hunting 1.1.0 visible satellite pass prediction shareware available for download at [Satellite Hunting](http://stephen.fathom.org/sathunt.html) ---
**Author:** ![Sofa\_King](https://avatars.discourse-cdn.com/v4/letter/s/58956e/32.png) [@Sofa\_King](https://boards.straightdope.com/u/Sofa_King)\ **Post date:** [December 16, 1999, 8:26pm UTC](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412/31 "1999-12-16T20:26:00Z")
You don’t need a big EMP to kill the ignition on a car. You just need to emit a modestly strong frequency tuned to the ignition of the particular make and model of the vehicle. There’s an old urban legend that for a period of time Jaguar XKEs on the Santa Monica Freeway would stall at the same point on the road. Supposedly, this was a result of an electronics manufacturer testing its products at the identical frequency the Jag’s ignition system ran at. A little bit of interference was all it took to make the car lose its ignition timing and stall. Of course, Jaguars relied on electrical equipment supplied by [thunderclap] **Lucas, Prince of Darkness** [/thunderclap]. Modern vehicles might not be so susceptible to such interference. ---
**Author:** ![JoeyBlades](https://avatars.discourse-cdn.com/v4/letter/j/a87d85/32.png) [@JoeyBlades](https://boards.straightdope.com/u/JoeyBlades)\ **Post date:** [December 17, 1999, 2:46pm UTC](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412/32 "1999-12-17T14:46:00Z")
Stephen, You wrote: > [@](#): > > But then, only if you tried to lock them up. ABS ‘pulses’ the brakes when you are braking hard enough to cause your tires to slip. ABS does nothing during normal stops. We’re getting slightly off-topic here, but just thought I should clear things up. ABS sometimes means Anti-lock Braking Systems and these function by sensing when your wheels’ rotation and releasing the brakes for a small interval so that the wheel can turn again, essentially pumping your brakes when you go into a skid. Rolling friction is more effective and controllable than skidding friction. Contrary to popular attention, you don’t have to slam on your brakes to be in a skid condition where your anti-lock braking system kicks in. It can happen on ice, wet pavement, and loose gravel. Sometimes ABS means Automatic Braking System, which contains anti-lock functionality, plus more. Automatic braking systems anticipate skids before they occur, compensate for the effects of turns, adjust braking pressure to each wheel based on the weight and center of gravity of the vehicle, compensate for four wheel drive, compensate for when the engine is not running, etc… ---
**Author:** ![JoeyBlades](https://avatars.discourse-cdn.com/v4/letter/j/a87d85/32.png) [@JoeyBlades](https://boards.straightdope.com/u/JoeyBlades)\ **Post date:** [December 17, 1999, 3:10pm UTC](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412/33 "1999-12-17T15:10:00Z")
Yikes! Chaos Grammatik. I wrote: > [@](#): > > …these function by sensing when your wheels’ rotation and releasing the brakes for a small interval… It should probably have been something like: …these function by sensing the rotation of the wheels and releasing the brakes for samll intervals when the wheels lock… ---
**Author:** ![APB9999](https://avatars.discourse-cdn.com/v4/letter/a/8e8cbc/32.png) [@APB9999](https://boards.straightdope.com/u/APB9999)\ **Post date:** [December 17, 1999, 9:18pm UTC](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412/34 "1999-12-17T21:18:00Z")
Okay, I asked a physicist friend about this. The conversation went something like this [I explained the basic idea] Me: So, is it feasible? P: Maybe. The easiest way to think about an electromagnetic pulse is that it is a _piece_ of an electromagnetic wave. Or, simply, a wave that only lasts for one cycle. Me: So you could direct it. P:Sure. Well…it would depend on the wavelength. If it was a very sharp spike, an X-ray spike, it would pass through most materials, but it would hard to make an X-ray pulse anyway. If it was of a wavelength that made it radio or microwave length then of course you could focus with any ordinary antenna generally used for that purpose. Me: So how do you make a pulse without a nuclear bomb? P: It’s an issue of power. Pulses that are strong enough to interfere with electronics are rare, though nuclear devices DO create them. That’s what most people mean when they say “electromagnetic pulse”. But you could create a lower power pulse just by creating a high voltage and then rapidly discharging it to ground. I doubt that would be powerful enough to interfere with a car under most … Me: (warming to the topic) While surely that just depends on the _amount_ of voltage you use. And a cruiser wouldn’t have to carry the power source with it! You could charge a capacitor at a high voltage source and then carry the cap with you. P: (starting to get bored) Yeah, sure. You got any pretzels? M: (getting excited, and feeling all smug and vindicated) So all we really need to know is how small a pulse will interfere with a car engine, and we don’t have to fry the electronics, of course, just degrade performance enough that the car won’t go very efficiently. P: (losing interest) Yes. But I’m not really an auto mechanic, so I don’t know what those numbers are or if it would be feasible given size and weight constraints on the device. You need to ask an automotive engineer how small a pulse is problematic. You know, pretzels are nothing without beer. So that’s where I am now. The only thing I would add, in response to some of the objections here is that this need not be a PERFECT technology, or even a PERFECTLY SAFE one. It only needs to be BETTER and SAFER than the current approach to the problem, which is for cops to take off after the fleeing car at speeds as high as the cars go, with all the danger that entails to innocent bystanders. I’ve watched a grand total of two of those tv shows where cops chase people, and in one the cops stopped a car with a strip across the road with spikes sticking up to destroy the tires. This was, of course, after they had cleared all the traffic off several miles of interstate. In the other - I kid not - a cop stuck his torso out the window and tried to SHOOT OUT THE TIRES with his revolver (after getting radio permission from HQ). I was very surprised by this, as it seems more like a movie device than anything I’d expect to happen on a real highway. He missed, by the way. Oh and Stephen, since my last post you’ve put up some better arguments. I’ll think about them. Thank You. ---
**Author:** ![Stephen](https://avatars.discourse-cdn.com/v4/letter/s/96bed5/32.png) [@Stephen](https://boards.straightdope.com/u/Stephen)\ **Post date:** [December 18, 1999, 1:11am UTC](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412/35 "1999-12-18T01:11:00Z")
Sorry if my posts were taken wrong. I don’t think I meant to offend (though I have been running ragged to clear my workload before the holdays, so I may have been irritable). One more fly for the ointment. If you figure out a minumum energy for interfering with a car and you determine it is ‘directable’, you also have to figure out how you’re going to get it into the sheetmetal ‘reflector’ presented by the offending car’s body. The thing that makes a ‘real’ EMP so damaging, is that it is broadband and permeates practically everything. If you take those properties away, in order to prevent problems with the ‘host’ vehicle, you will also be limiting the impact on the bad guy’s car. This is why I threw my hands up, when you rejected proximity as a solution. * * * Stephen [Stephen’s Website](http://stephen.fathom.org) Satellite Hunting 1.1.0 visible satellite pass prediction shareware available for download at [Satellite Hunting](http://stephen.fathom.org/sathunt.html) ---
**Author:** ![kuwatto](https://avatars.discourse-cdn.com/v4/letter/k/6a8cbe/32.png) [@kuwatto](https://boards.straightdope.com/u/kuwatto)\ **Post date:** [December 18, 1999, 6:11am UTC](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412/36 "1999-12-18T06:11:00Z")
Call me crazy, but a “real EMP” would create a traffic jam around a suspect blocking him from escaping, regardless of how vintage his car or motorcycle is. Dozens of cars slowly rolling to a stop, instead of a high speed chase? ---
**Author:** ![Diceman](https://avatars.discourse-cdn.com/v4/letter/d/22d042/32.png) [@Diceman](https://boards.straightdope.com/u/Diceman)\ **Post date:** [December 20, 1999, 6:02am UTC](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412/37 "1999-12-20T06:02:00Z")
…and then dozens of people would sue the poice for frying their vehicles’ electronics. That, I believe, is the crippling limitation to EMP technology. Conventional police chases _sometimes_ end in civilian damages and injuries. But an EMP pulse would _almost always_ create significan damage. And what if somebody nearby has a pacemaker? You’d kill a civilian anyways. [Previous page](https://boards.straightdope.com/t/whacko-suggestion-for-stopping-a-car/5412.md?page=1)