Marijuana DUI

[roo_ster]

http://www.nytimes.com/2014/02/18/health/driving-under-the-influence-of-marijuana.html?ref=science&_r=0

If you are pulled over on suspicion of drunken driving, the police officer is likely to ask you to complete three tasks: Follow a pen with your eyes while the officer moves it back and forth; get out of the car and walk nine steps, heel to toe, turn on one foot and go back; and stand on one leg for 30 seconds.

Score well on all three of these Olympic events, and there’s a very good chance that you are not drunk. This so-called standard field sobriety test has been shown to catch 88 percent of drivers under the influence of alcohol.

But it is nowhere near as good at spotting a stoned driver.

Article is about the problems of an accurate tool to determine DUI of JM, but what struck me was the part I put in bold face: "This so-called standard field sobriety test has been shown to catch 88 percent of drivers under the influence of alcohol."

OK...what about false positives? 

The number of false positives (N =24) was much greater than the number
of the false negatives (N =4).
In the range of data near the 0.08% level, the estimated BAC by these
experienced officers overestimates the measured BAC, introducing
a bias against the subjects (see Fig. 1). Using EBAC to determine
whether the subject MBAC is greater than 0.08% is 100% accurate
for all subjects with MBAC > 0.12%. In other words, if the subject
is highly intoxicated, the SFST provide an accurate indication. It
is not surprising that if the subject is clearly intoxicated, the offi-
cers can make this determination. If the MBAC is < 0.08%, there
is a 24/(24 + 59) = 29% chance of a false arrest (determined from
Fig. 2).

Why a 29% of false arrest?  Why 6x as many false positives as false negatives?   I can think of several:
1. LEO has already pulled you over and invested time/effort he wants to pay off.
2. No consequences for false positives, real consequences for false negatives (time, opportunity, and possibility DUI-er runs into a bus load of hemophiliac orphans down the road).

[Nick1911]

Honestly, with the wide availability of cheap, portable analytically chem equipment, I see little place for subjective evaluation techniques.  Fluke equipment once had a motto I liked: "If you don't measure, you don't know."

[Fitz]

Honestly, with the wide availability of cheap, portable analytically chem equipment, I see little place for subjective evaluation techniques.  Fluke equipment once had a motto I liked: "If you don't measure, you don't know."

Tough with MJ. The THC stays in your system long after the negative influence on your abilities have passed

[cordex]

SFSTs for alcohol are usually used in conjunction with a non-admissible Portable Breath Test. Failing either can lead to admissible tests (blood or breath).  They mostly serve to establish probable cause for the real tests.

As I recall, roadside indicators for pot involve looking for very red conjunctiva and something else having to do with the eyes - a twitching of some sort, I will ask tonight if I get a chance. Both can tell generally how long since pot was last used but not how impaired the subject is.

[Firethorn]

Both can tell generally how long since pot was last used but not how impaired the subject is.

Part of the problem with this is that research into 'driving while stoned' is both rare and has shown mixed results on showing actual impairment.  IE it's been shown in at least one study that a regular user is actually a BETTER driver while slightly high than when completely sober.

As for the pot tests, I figure it's mostly because they've been looking for tests that can tell if you've been using for a while, because use was completely illegal, so a test that could determine use over a longer period was desired, vs now they have to look for one that shows actual intoxication.

[dm1333]

As I recall, roadside indicators for pot involve looking for very red conjunctiva and something else having to do with the eyes - a twitching of some sort, I will ask tonight if I get a chance. Both can tell generally how long since pot was last used but not how impaired the subject is.

If you are talking about HGN (horizontal gaze nystagmus) when you say "twitching", it doesn't work for pot, only alcohol.

[RoadKingLarry]

Many years ago when we lived in a ground floor apartment in El Cajon we could sit on our front "porch" and watch the traffic go by. One evening I witnessed a collision at the intersection, guy just drove into the back of the car stopped at the light. (Nobody was hurt) I sat there and watched the cops administer the field sobriety test. Now it's possible that since it was pretty obvious that the driver seriously impaired/intoxicated the cops were screwing with the guy some but some of the stuff they were throwing at him would have been a challenge for me stone cold sober.

Say the alphabet backwards starting with R.

[Northwoods]

In WA they set a standard for impairment with pot.  I forget the actual number, but it worked out that to fail that test you had to have smoked pot recently enough to still be "high" and presumably actually impaired.  There's chemicals they can test for that have a pretty short half life in your blood stream that prove recent consumption.  Most of the THC tests people think of are able to detect use within the last month or two (or whatever) but that is not what they use for DUI-Doobie charges.

[cordex]

If you are talking about HGN (horizontal gaze nystagmus) when you say "twitching", it doesn't work for pot, only alcohol.

Nope, a different twitch. The test is to have the subject close their eyes and tilt their head back. The eyelids will twitch when the subject is still under the influence of THC. 

[T.O.M.]

If I remember correctly,  pot causes vertical nystagmus,  not horizontal...

I seem to recall reading about a study in California of the impact of pot on driving.  A surprising number orbtest subjects drove better afyer pot use.

[SADShooter]

If I remember correctly,  pot causes vertical nystagmus,  not horizontal...

I seem to recall reading about a study in California of the impact of pot on driving.  A surprising number orbtest subjects drove better afyer pot use.

How well did they type?

[T.O.M.]

Better than I do on this damn virtual keyboard, I'm sure.   

[freakazoid]

SFSTs for alcohol are usually used in conjunction with a non-admissible Portable Breath Test. Failing either can lead to admissible tests (blood or breath).  They mostly serve to establish probable cause for the real tests.

As I recall, roadside indicators for pot involve looking for very red conjunctiva and something else having to do with the eyes - a twitching of some sort, I will ask tonight if I get a chance. Both can tell generally how long since pot was last used but not how impaired the subject is.

You planning on getting smoking and then getting caught while driving?XD

[cordex]

You planning on getting smoking and then getting caught while driving?XD

I do what I have to do for APS.

[roo_ster]

I do what I have to do for APS.

Better you than me.  MJ is some stinky stuff.

[Ned Hamford]

I'd toss out the laws for driving impaired and just have them as aggravations for the base charge of reckless driving.  Oh to imagine how much simpler the world would be.  I haven't done any DWI cases lately, but my opportunity for error count for the system in place in NY 5 years ago was 64; Officers have enough on their plate and can't be expected to be chemists too.  Protect and Serve > Seize+Revenue

[roo_ster]

I'd toss out the laws for driving impaired and just have them as aggravations for the base charge of reckless driving.  Oh to imagine how much simpler the world would be.  I haven't done any DWI cases lately, but my opportunity for error count for the system in place in NY 5 years ago was 64; Officers have enough on their plate and can't be expected to be chemists too.  Protect and Serve > Seize+Revenue

That makes a whole lot of sense.