Technology Could End Drunk Driving

[Double Mocha Man]

25 minutes ago, David in FL said:

It’s only one aspect of excessive speed which kills. Excessive speed too fast for the conditions, type of surface, visibility due to terrain, radius of curves, proximity to pedestrians, and many more, are all factors that can contribute to speed related accidents.

And no, I don’t want my car limited in that manner either...

You could reduce ALL alcohol related driving deaths by banning cars too.  But that  wouldn’t be a reasonable solution either...

Disagree.  I feel, in reading the article, they are trying to come up with a reasonable solution.  Guessing your reasonable isn't my reasonable.  Banning all cars would be like banning all golfers, to put an end to shanks.  It's a joke.  It's a joke.  I'm required to use smiley faces these days because my humor is too subtle.😀😊😊😀 

[Vinsk]

1 hour ago, Double Mocha Man said:

  I feel, in reading the article, they are trying to come up with a reasonable solution. 

Sometimes when dealing with human beings, the only solution is to realize there isn’t one. Not reasonable at least. Sometimes we have to rely and just hope to minimize the collateral damage from ignorance. People still get mauled at zoos, fall off touristic scenic views, die from swimming out too far, overdose on OTC meds and keep venomous snakes as pets. Sadly people become victims of Darwinism or evil. 

[Patch]

I am reading alot of replies in this thread, that are speculative at best. I say speculative because, unless you personally have lived through a car wreck caused by a drunk driver, I consider any answr to be speculation by those who have been fortunate. Knock on wood. .

Let me ask a speculative question.

As "no" voter, if you were to lose an immediate family member, relative, even a great friend to a drunk driver, knowing that legislative technology could have prevented your loss, would you change your vote?

Edited October 17, 2019 by Patch

[iacas]

7 minutes ago, Patch said:

I am reading alot of replies in this thread, that are speculative at best. I say speculative because, unless you personally have lived through a car wreck caused by a drunk driver, I consider any answr to be speculation by those who have been fortunate. Knock on wood. .

Let me ask a speculative question.

As "no" voter, if you were to lose an immediate family member, relative, even a great friend to a drunk driver, knowing that legislative technology could have prevented your loss, would you change your vote?

No. And you seem to be making a bunch of assumptions yourself.

[Vinsk]

12 minutes ago, Patch said:

I am reading alot of replies in this thread, that are speculative at best. I say speculative because, unless you personally have lived through a car wreck caused by a drunk driver, I consider any answr to be speculation by those who have been fortunate. Knock on wood. .

Let me ask a speculative question.

As "no" voter, if you were to lose an immediate family member, relative, even a great friend to a drunk driver, knowing that legislative technology could have prevented your loss, would you change your vote?

I don’t have to experience a tragedy or evil wrongdoing to recognize it as tragic and/or evil. 

[Pretzel]

6 hours ago, Braivo said:

FWIW we submit ourselves to security checks at airports to avoid something (terrorism) that has caused a total of 3k-4k deaths total, ever. Yet we are concerned about giving up some freedom that could save that many lives per year, or more!

FWIW the TSA is absolute garbage that literally can't do their job even in their own tests. 

'Disturbing' undercover probe found TSA screeners missing many test weapons

---

A Congressional committee chairman said a classified briefing on vulnerabilities in airport security was "disturbing."

 They fail to find 95% of weapons, which makes your argument in favor of this using the TSA as an example even more ridiculous. It's like saying we should go over Niagara Falls in a barrel by pointing to Annie Edson Taylor and ignoring all the times that it doesn't work.

6 hours ago, Braivo said:

I must point out that using statistics in this manner is an absolute disgrace. Auto crashes are the leading cause of death for many age groups, particularly young people in their late teens and early 20s. Most of these deaths are far more tragic than heart disease and diabetes at older ages. Auto crashes are the biggest threat to the lives of my children and driving is by far the most dangerous thing each of us does each and every day. 

The only thing disgraceful here is the spouting of outright lies about the leading causes of death. Your claimed statistics are patently untrue, and yet you think the facts of the situation are somehow disgraceful? The facts don't care how you feel, but they do guide people towards the most effective course of action in every scenario.

Preventable causes of death - Wikipedia

Among preventable causes of death all traffic accidents are ranked 7th and make up only 1.8% of total deaths in the US annually. Among all causes of death globally road traffic accidents are only ranked 19th.

 

[jsgolfer]

On 10/16/2019 at 8:16 PM, billchao said:

Aren't Americans pretty resistant to self-driving cars? Freedom of the open road and all that. I don't think self-driving cars are going to be mainstream anytime soon.

But you or a loved one can still be killed by someone else who does. I don't think the proposed legislation is aimed at eliminating drunk driving 100% but if it can reduce the number of drunk drivers on the road it's a step in the right direction.

If it's something simple and built into the push start button on a car, I don't think it's going to take any extra effort on your part to start it. The issue is more about how reliable the system can possibly be and what happens if/when it fails.

And you or a loved one could get killed by someone running a red light, making sudden lane changes at a high rate of speed, texting, falling asleep at the wheel or a myriad of other distractions.  If your loved one died due to these would it not be as tragic, or is it only if alcohol is somehow involved, then it makes it worse?  

On 10/16/2019 at 8:30 PM, Pretzel said:

This is entirely irrelevant and making laws based on how you personally feel about events is the quickest way to create stupid and ineffective laws. Emotions are never rational and can never come up with logical and effective solutions. Laws like the creation of the TSA, which has been found in numerous independent tests (and even their own self-testing) to be entirely ineffective at actually finding weapons.

I'm an Electrical and Computer Engineer in the biomedical device industry, I know far more about the technology behind these devices than the average person. "Almost impossible to trick them with gloves or a buddy pushing the button" would imply that you must have continuous contact with your skin to continue driving. Congratulations, you now are no longer allowed to drive a car with gloves on in the winter. You also get to face the problem of not being able to drive the car when your hands are cold because the reduced bloodflow to your fingers will confuse the device and throw an error similar to if you had gloves on. In other words, your car no longer works as a car when it's cold out.

No new technology will stop them, because people who drive drunk can still obtain one of the tens of millions of old cars without this technology.

+1 - Once emotions get in anything bad laws are sure to follow.  

9 hours ago, Braivo said:

I must point out that using statistics in this manner is an absolute disgrace. Auto crashes are the leading cause of death for many age groups, particularly young people in their late teens and early 20s. Most of these deaths are far more tragic than heart disease and diabetes at older ages. Auto crashes are the biggest threat to the lives of my children and driving is by far the most dangerous thing each of us does each and every day. 

Also, someone drinking themselves to death with soda doesn't kill other innocent people. Everything about your logic is wrong. 

FWIW we submit ourselves to security checks at airports to avoid something (terrorism) that has caused a total of 3k-4k deaths total, ever. Yet we are concerned about giving up some freedom that could save that many lives per year, or more!

Anything that has a chance to reduce this risk should be explored imo. I generally do not like to give up "freedom" for security, but am willing to make some compromises to mitigate the risk of auto crashes. 

 

Auto crashes may be the biggest threat to children, but that wouldn’t be from drunk drivers killing them.  Lots of innocent people get killed in auto crashes every year, not all are killed by drunk drivers.  I’ll pose a question to all who said yes to the post, if all drunk driving fatalities are unavoidable if the person who is drunk didn’t drive, why are there any other traffic fatalities? Obviously if you haven’t been drinking you should never get in an accident?  

I don’t agree that it will save that many lives.  I believe there are something like 6,000 traffic fatalities during sunrise and sunset, when visibility is poor.  Why don’t we ban driving during these times?

8 hours ago, chspeed said:

Sure, if you use safer as an absolute term. We all know that everyone cherry-picks the statistics they care about. I can tell you that 61% of motor vehicle deaths involve alcohol (real number). People fight for stuff they care about. I'm not sure what headlines you're reading, but I haven't seen an article about drunk driving in national news in many years.

You’re 61% number is incorrect.  And I posted this on another thread a couple of years ago and @iacas mentioned it already, but I’ll go ever further then he did, not only are more than 50% of all alcohol-related fatalities a single car crash, killing the driver and occupants with them, but not all alcohol-related fatalities mean that the person driving was impaired.  An alcohol-related fatality is if anyone in the car has alcohol in their system.  So a Designated Driver could be in a traffic fatality with 3 drunk passengers and this is 4 people involved in an alcohol-related fatality. Or you could have a beer and some dope runs the red light hitting you and causing a fatality, but you being a driver and having alcohol in your system are probably going to be the one who goes to jail.

8 hours ago, Double Mocha Man said:

And again, personally, I will accept the inconvenience and related costs to keep the road safer than it is now... for me, my loved ones and everyone on this forum. 

Oh, and it is something, like other safety devices, that will be phased in over the years.  So if you have an older car you'll be exempt.  But over 15 years a very high percentage of cars need to be replaced.  Like seat belts, eventually they showed up on most cars, except classics.

I’m glad you’ll accept the inconvenience, I’m not.Plus you’re not going to phase out all older cars in 15 years.  

8 hours ago, Patch said:

I voted "yes". Didn't even give that vote a second thought. 

I am one of the very few on this forum that has first hand knowledge of the pain, and misery a drunk, or other wise impaired driver can cause. 

Sorry for your loss, but same question as before, would you feel any different if it was a red light runner that caused the same pain?  Not to be callous, just what is the difference.

8 hours ago, Braivo said:

Guys hit in head with golf ball per year when standing too far forward of the tee: 10?

People KILLED as a result of drunk driving: 10,000!

Not an appropriate comparison. 

As stated before, more than 50% of the 10,000 are the drivers of the vehicles.  

6 hours ago, Double Mocha Man said:

Up to this point the discussion has referred to "bricking" the car as meaning shutting it off while in the driving mode.

If you fail the test (before any tires are rolling) you are probably over the limit in terms of alcohol in your system.

With all due respect it comes down to this:  Many of you are saying you'd rather people die than you personally having to give up a small right/convenience.  I am sorry to say that but look closely at your arguments.  I do like this site and wish to continue posting on it so I hope this statement doesn't get me banned.

I think a lot of good folks in this excellent forum are reaching at straws to try to support their position.  If you don't like having someone tell you what to do just say so... don't trump up weak arguments.

Et tu Brute....

5 hours ago, iacas said:

A few quick hits.

I disagree. You're talking about inconveniencing millions of people.

Auto deaths per year in the U.S.: ~37,000.
Auto deaths involving alcohol: ~10,000.

That's under 30%, and most of those are the driver.

Very few of them are alcohol-related.

If you want to say we should push back the driving age to 21 or 25 or something, you might be able to make a good case for it using these stats.

How often are your kids out between the hours of 10pm and 4am, when most alcohol-related accidents happen?

I agree, keeping them safe between the hours of 3pm to 6pm goes up if they're in a car (rush hour), but that's just automobile accidents. This type of device, when functioning properly, will have basically ZERO effect there. None. Except for the few bricked cars non-intoxicated people can't start. 😛 And then when they can get it to start, maybe they'll cause more accidents because they're now late.

Here's another stat for you: ~3500 deaths are caused by drowning in pools every year. About 1/3 as many as alcohol-related automobile accidents. And far, far, far fewer swim in pools, and do so far, far, far less often than they drive or are driven around.

It's still the real world. A device that works 99% of the time is unacceptably bad. "As expected" is not going to be 99.999% of the time with virtually no false negatives.

No, it's not. One such reason why that's a poor analogy: choosing not to wear a seat belt doesn't brick your car. It doesn't stop you from going anywhere. You don't have to click your seat belt properly in order to go somewhere, physically, in your car.

I don't think that number is at all correct. I think it's under 30%.

Why should I have to? And you've done nothing to address false positives, false negatives, failure rates (again, 99% is NOWHERE near effective - there's a reason these devices are only installed in the cars of prior convicted drunk drivers - they've lost the right to have a car that is guaranteed to work all the time. I have not.)

No, you're completely incorrect. It means rendering the car inoperable by failing the test. It means you cannot drive the car.

No, it doesn't absolutely mean that. "Probably" had better be accurate to about 99.9999% certainty, or it's unacceptably high.

Uhm, no, it isn't saying that. At all.

That's one of the more ridiculous comments you've made.

---

I'll end with this, and point out that what we're doing is working pretty well, it appears, and that this is an unnecessarily HUGE step that annoys and costs EVERYONE:

Drunk Driving Fatalities

---

Though progress has been made, our commitment to eliminate drunk driving is stronger than ever. Visit us for facts and statistics on drunk driving fatalities.

 

+ A Bunch......

5 hours ago, iacas said:

It does not change my vote.

I didn't spend a ton of time looking into it, but it seems from a few sites that about 60-65% of the deaths in alcohol-related auto accidents are the driver. Another 20% are the passenger of the driver responsible (or irresponsible) for the crash, and another good chunk are motorcyclists. Surprisingly (to me anyway) few "other" people (innocent persons being on the road at the wrong time) are killed by drunk drivers.

And that "wrong time" is basically the middle of the night. The odds of dying - when you're not the drunk driver himself - at 10am on a Tuesday are pretty freaking slim. Or 2pm on a Thursday. Or whatever.

If you're a drunk driver that's drunk and driving between 9pm and 3am, then yeah, odds go up that you're gonna kill yourself. But you're probably not gonna kill anyone who's just standing around, because there are not actually many people just standing around between those times.

And it might keep me off the road because it fails, or make me late for a meeting, or a wedding, or to catch a flight, and cost me a thousand bucks to have repaired, or… or… or…

I see little point in playing games with stories. They're emotional, and you can make them up just like I could make up stories about how inconvenient, costly, detrimental, etc. these could be.

Also, I notice how you gloss over the stuff that's inconvenient to you, like your complete misunderstanding of the word "bricked."

---

In short… punish those who break the law, and let the punishments of those serve as a deterrent to others. Any and all reasonable measures to curb drunk driving (or bad driving in general), I'm in favor. But this isn't, IMO, reasonable.

And that's all it boils down to, really. We disagree on whether this is reasonable or not.

+ A bunch More...

2 hours ago, Patch said:

I am reading alot of replies in this thread, that are speculative at best. I say speculative because, unless you personally have lived through a car wreck caused by a drunk driver, I consider any answr to be speculation by those who have been fortunate. Knock on wood. .

Let me ask a speculative question.

As "no" voter, if you were to lose an immediate family member, relative, even a great friend to a drunk driver, knowing that legislative technology could have prevented your loss, would you change your vote?

No, my vote would not change in the least.  

Most people that cause alcohol-related fatalities are people with BAC around 0.15, almost twice the legal limit.  With as many Bars, wineries, distilleries, breweries, restaurants and how prevalent alcohol is, it’s amazing how safe it is on the roads or is it really becasue it’s not as much of a threat as the media and the government make it out to be.  

I think @Pretzel said it great, emotions = bad laws.  

Edited October 18, 2019 by jsgolfer

[billchao]

5 minutes ago, jsgolfer said:

And you or a loved one could get killed by someone running a red light, making sudden lane changes at a high rate of speed, texting, falling asleep at the wheel or a myriad of other distractions.  If your loved one died due to these would it not be as tragic, or is it only if alcohol is somehow involved, then it makes it worse?  

I'm not really sure why you quoted me there and then wrote this. None of this has anything to do with anything I wrote in this thread. The next time I write the word "tragic" here will be the first.

[David in FL]

3 hours ago, Patch said:

 

As "no" voter, if you were to lose an immediate family member, relative, even a great friend to a drunk driver, knowing that legislative technology could have prevented your loss, would you change your vote?

Absolutely not.

Sadly, sometimes bad things happen.  While it’s easy to say that doing anything that prevents some of those bad things must be good, emotion can cloud the ability to appreciate other serious, unintended consequences that may arise in implementing those things.

[dennyjones]

7 hours ago, David in FL said:

Along similar lines.  A simple governor will limit top speed too.  Since we know that excess speed kills, why not limit all cars to the speed limit?  Hell, with gps, it could easily be road/street specific.  Even school zones could be programmed in.  

I see little difference between the two, except the speed limitation would likely be more reliable... 

This is already in the works with autonomous vehicles.

[David in FL]

5 minutes ago, dennyjones said:

This is already in the works with autonomous vehicles.

Not the same thing at all though, and the technology to limit speed based upon your current location is simple, and already exists.  

[Lihu]

5 hours ago, Patch said:

I am reading alot of replies in this thread, that are speculative at best. I say speculative because, unless you personally have lived through a car wreck caused by a drunk driver, I consider any answr to be speculation by those who have been fortunate. Knock on wood. .

Let me ask a speculative question.

As "no" voter, if you were to lose an immediate family member, relative, even a great friend to a drunk driver, knowing that legislative technology could have prevented your loss, would you change your vote?

I lost my sister in law and a cousin to drunk drivers and know quite a few others who have lost family.

Drunk driving is stupid. The question is if we all should pay for that stupidity or not? We live with quite a few laws already because stupid people did stupid things like drunk driving, I’m not sure another law would hurt?

OTOH, drunk driving isn’t the only problem.

What I think would make more sense is mandatory automatic braking systems and enforced speed limits through GPS. The first step towards self driving cars. Something like that, but thought through thoroughly before deployment.

I answered to add vehicle safety, but I can understand the arguments against.

[uitar9]

vote was yes. My guess is that the non alcoholics all voted no.

Drunk driving laws are like locks...they work for honest folks.

If I drink, I will probably drink and drive...so I have stopped drinking. Once I black out all bets are off. 

 

[Pretzel]

8 hours ago, Lihu said:

What I think would make more sense is mandatory automatic braking systems and enforced speed limits through GPS. The first step towards self driving cars. Something like that, but thought through thoroughly before deployment.

I'd go with this system over either of those. I have seen automatic braking systems malfunction before and it turns catastrophic in an instant. The incredibly unfortunate part is that automatic braking systems also have a disturbingly high number of ways they can be fooled. The two I have seen personally were leaves covering up the sensor (slammed the brakes on someone in town and caused a collision) and bugs from I-70 covering the sensor (the car locked up and the brakes remained engaged until the sensor covering could be cleaned).

As far as GPS-enforced speed limits, this also introduces danger on the roads. It prevents drivers from making effective evasive maneuvers when driving at the speed limit. Malfunctions for this system would also be incredibly dangerous, considering the number one cause of traffic accidents is a differential in speed between the two cars that collided. If one car is limited to 10mph under the speed limit because their GPS glitched out then they just became a sitting duck on the road, though not as bad as the automatic braking malfunction.

I'm fine with mandatory safety measures that don't risk lives compared to the alternative of not having them, such as seat belts and air bags. If those fail you may die, but if they fail you are no worse off than you would have been if the safety measures were never installed.

I draw the line at mandatory safety measures that will actively risk your safety or life when they fail. Automatic braking systems that will slam the brakes in highway traffic. GPS-enforced speed limits that can hamper evasive maneuvers and cause the same symptoms as automatic braking system failures (if an error displays a limit lower than the true limit). And yes, mandatory BAC interlock devices for law-abiding citizens that can leave them stranded and stuck with a very costly repair bill in the best case scenario and death in the worst case scenario.

If we want to talk about personal anecdotes about why it's incredibly important to be able to start you vehicle at any time, I've got the perfect example of how this can risk lives in real scenarios that actually happen.

When I was 17 I took the bus with my friends down to the annual Denver Avalanche game and we hung out at the 16th Street Mall afterwards until we caught the last bus back to where our cars were parked. Having parked in opposite corners we parted ways getting off the bus and went to our cars, my friends having no issues driving home. I, on the other hand, had some trouble with starting my vehicle. You see that year the temperature was 15 degrees below zero and my car was an old (1979) Mercedes 240D diesel. Diesel engines don't particularly like the cold, so I cycled the glow plugs several times before trying to start. No dice, so I repeated that. This went on until my car battery died at around 2 AM, and the worst part of it was that stupidly I was only wearing jeans, a t-shirt, and a sweatshirt with no jacket or coat. The buses had finished their schedules and the park and ride was empty (I was the last car) in the middle of nowhere without areas I could take shelter nearby. I was lucky to have a mylar blanket and a comforter in the trunk of my car that I kept there only because my Grandpa insisted I'd need them if I was ever stranded in the cold.

I wasn't able to get assistance at my location until 5:30 that morning because it was located in the mountain, a lovely cell phone dead zone. 3.5 hours spent in -15 degree weather with only jeans and a sweatshirt. Even sitting in my car without exposure to wind I would have risked frostbite in 30 minutes or less, and that temperature presents a high risk of hypothermia even with proper winter clothing. While wearing winter clothing at that temperature you'll lose one degree of core body temperature about every 30 minutes, sooner if you have no hat. Below 95 degrees (2 hours) is the beginning of hypothermia, below 93 degrees (3 hours) is when amnesia sets in. Profound hypothermia is 90 degrees (4.5 hours) and you'll find yourself no longer even shivering to keep warm. At 86 degrees (6.5 hours) your heart starts to pump arrhythmically. At 85 degrees (7 hours) you'll rip off your clothes for your final minutes of life. Those times are for proper winter clothing.

When an ignition interlock device fails, it WILL kill people in the mountains every single year. People who went camping, skiing, hiking, or hunting and get back to their car in the evening only to have it refuse to start. Cell service is sparse at best in these areas, meaning only those prepared with extra blankets/gear and the ability to start fires will survive through the night without heat from their vehicle. I say when, not if, because the failure rate will be above 0%. 15 million new cars are sold each year, and if the failure rate is 0.01% annually then you'd see 1,500 failures in the first year, growing by another 1,500 every year and providing 1,500 more opportunities to kill in either what was described or other scenarios.

---

This is exactly why using emotional arguments is dumb, because realistically the number of deaths would be small but a personal anecdote carries additional weight. The point is that any deaths that directly result from a safety device are unacceptable even if that safety device may save lives in other circumstances. Trading lives of innocent and law-abiding citizens because of a small number of criminals is morally reprehensible on every level.

[DeadMan]

I thought about this a while, and then had an epiphany last night.  Without a perfect test, the answer is almost definitely no. It's a fairly simple statistical calculation called Bayes' Theorem. The end result is that you'll end up preventing more people from driving when they aren't drunk than preventing drunk drivers.

I'm going to plug in numbers, but since I'm (likely correctly!) assuming drunk driving is a rare event, the numbers don't really matter that much. I'm also going to assume the test is extremely accurate.

Let's say that in 1/10,000 car trips, the driver is too drunk to legally drive. This is probably an underestimation by a factor of 100, if not more, if you think about how many car trips there are in a day. Let's assume that the when the test is positive, the driver is drunk 99.9% of the time. And then assume that when the test is negative, the driver is sober 99.9% of the time (in other words, if the test is negative, the driver is drunk 0.1% of the time).

We can use this to plug in probabilities for each event.

Probability that a driver is drunk: .0001

Probability that a driver is sober: .9999

Probability that a drunk driver gets a positive test: .999

Probability that a drunk driver gets a negative test: .001

Probability that a sober driver gets a positive test: .001

Probability that a sober driver gets a negative test: .999

Bayes' Theorem applies here. It says:

The probability that someone is drunk driver given a positive test is equal to the probability of a drunk driver gets a positive test times the probability of a drunk driver; that divided by the following: the probability of a drunk getting a positive test times probability of a drunk driver plus the probability of sober driver getting a positive test times the probability of a sober driver.

In mathematic terms (DD=drunk driver; SD = sober driver; + = positive test):

P(DD | +) = (P(+ | DD)*P(DD))/((P+ | DD)*P(DD)+P(+ | SD)*P(SD))

Plug in the numbers:

P(DD | +) = ((.999)*(.0001))/((.999)*(.0001)+(.001)*(.9999))

P(DD | +) = .0908

In other words, the probability of a drunk driver given a positive test is only 9%. Meaning that out of a 100 people that test positive under this test, 91 of them would actually be sober.

Because the test is imperfect and drunk driving is rare, it's going to impact more sober drivers than drunk drivers. Even if the test is 99.99% accurate and as a false positive rate of 0.01%, the probability of a drunk driver given a positive test is only 50%. Note that I'm assuming that 1/10,000 car trips is one by a drunk driver. If you assume 1/100,000 car trips are by a drunk driver, the probability of a drunk driver given a positive test is 0.9%.

(You can also use this calculate to find out the odds that a drunk driver will have a negative test, but I have other stuff to do now...)

So, without a nearly perfect test, it's a bad idea for the entire population.

If drunk drivers were more frequent, then it would make more sense. Hence, it makes sense for someone who is more likely to drive drunk, and why the current policy probably makes sense. 

[Double Mocha Man]

25 minutes ago, DeadMan said:

I thought about this a while, and then had an epiphany last night.  Without a perfect test, the answer is almost definitely no. It's a fairly simple statistical calculation called Bayes' Theorem. The end result is that you'll end up preventing more people from driving when they aren't drunk than preventing drunk drivers.

I'm going to plug in numbers, but since I'm (likely correctly!) assuming drunk driving is a rare event, the numbers don't really matter that much. I'm also going to assume the test is extremely accurate.

Let's say that in 1/10,000 car trips, the driver is too drunk to legally drive. This is probably an underestimation by a factor of 100, if not more, if you think about how many car trips there are in a day. Let's assume that the when the test is positive, the driver is drunk 99.9% of the time. And then assume that when the test is negative, the driver is sober 99.9% of the time (in other words, if the test is negative, the driver is drunk 0.1% of the time).

We can use this to plug in probabilities for each event.

Probability that a driver is drunk: .0001

Probability that a driver is sober: .9999

Probability that a drunk driver gets a positive test: .999

Probability that a drunk driver gets a negative test: .001

Probability that a sober driver gets a positive test: .001

Probability that a sober driver gets a negative test: .999

Bayes' Theorem applies here. It says:

The probability that someone is drunk driver given a positive test is equal to the probability of a drunk driver gets a positive test times the probability of a drunk driver; that divided by the following: the probability of a drunk getting a positive test times probability of a drunk driver plus the probability of sober driver getting a positive test times the probability of a sober driver.

In mathematic terms (DD=drunk driver; SD = sober driver; + = positive test):

P(DD | +) = (P(+ | DD)*P(DD))/((P+ | DD)*P(DD)+P(+ | SD)*P(SD))

Plug in the numbers:

P(DD | +) = ((.999)*(.0001))/((.999)*(.0001)+(.001)*(.9999))

P(DD | +) = .0908

In other words, the probability of a drunk driver given a positive test is only 9%. Meaning that out of a 100 people that test positive under this test, 91 of them would actually be sober.

Because the test is imperfect and drunk driving is rare, it's going to impact more sober drivers than drunk drivers. Even if the test is 99.99% accurate and as a false positive rate of 0.01%, the probability of a drunk driver given a positive test is only 50%. Note that I'm assuming that 1/10,000 car trips is one by a drunk driver. If you assume 1/100,000 car trips are by a drunk driver, the probability of a drunk driver given a positive test is 0.9%.

(You can also use this calculate to find out the odds that a drunk driver will have a negative test, but I have other stuff to do now...)

So, without a nearly perfect test, it's a bad idea for the entire population.

If drunk drivers were more frequent, then it would make more sense. Hence, it makes sense for someone who is more likely to drive drunk, and why the current policy probably makes sense. 

Whew Dead!  Not sure if your statistics jive with this: Each day, people drive drunk more than 300,000 times, but only about 3200 are arrested.

 

Arrest data: Federal Bureau of Investigation, “Crime in the United States: 2014” https://www.fbi.gov/about-us/cjis/ucr/crime-in-the-u.s/2014/crime-in-the-u.s.-2014/tables/table-29 Incidence data: Centers for Disease Control and Prevention. “Alcohol-Impaired Driving Among Adults — United States, 2012.” Morbidity and Mortality Weekly Report. August 7, 2015 / 64(30);814-817. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6430a2.htm

[DeadMan]

4 minutes ago, Double Mocha Man said:

Whew Dead!  Not sure if your statistics jive with this: Each day, people drive drunk more than 300,000 times, but only about 3200 are arrested.

 

Arrest data: Federal Bureau of Investigation, “Crime in the United States: 2014” https://www.fbi.gov/about-us/cjis/ucr/crime-in-the-u.s/2014/crime-in-the-u.s.-2014/tables/table-29 Incidence data: Centers for Disease Control and Prevention. “Alcohol-Impaired Driving Among Adults — United States, 2012.” Morbidity and Mortality Weekly Report. August 7, 2015 / 64(30);814-817. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6430a2.htm

Uh, that doesn't say what you think it does.

[Double Mocha Man]

5 minutes ago, DeadMan said:

Uh, that doesn't say what you think it does.

Well, that's a hell of a lot of drunk drivers on the road at any given time.  Over 330 per hour, per state.