How to Create and Present Your Own Speed Survey

[lbk]

My question involves a traffic ticket from the state of: California (southern california)

I got a pacing 22350 ticket on surface streets. I am innocent. My core argument is that the speed I was going is "safe and prudent." The city's speed survey violates the MUTCD standards for speed surveys (among other problems) so the 85th percentile is skewed WAY too low; plus the survey was done in the middle of the week whereas I was ticketed on a Saturday morning when traffic is much lighter and prevailing speeds are much higher.

Doing my own survey (not as hard as you think) showed that my speed was below the 85th percentile for the conditions. Although I'm not a traffic engineer I have the technical credentials to conduct a survey that dramatically improved on the survey done by the city.

Questions:

1) What is the legal importance of an invalid prima facie speed limit in a pacing case?

From what I read, the only real effect is that it might technically shift the burden to the prosecution by removing the presumption of guilt. But, the officer admitted his judgment of safety was based on the speed limit alone (I was in the slow lane of a 4-lane road not passing anybody), so if the officer admits in court that his allegation of unsafe driving was based solely or primarily on the "invalid" prima facie limit, does this have weight? FWIW, the officer was CHP, and apparently not familiar with this city. I don't know why he was there.

2)

Is there a statutory, regulatory or other standard that establishes that the 85th percentile defines a "safe speed." This http://www.expertlaw.com/forums/showthread.php?t=117810 earlier thread says CalTrans defines the 85th percentile speed as safe, but I couldn't find it. Shouldn't it be sufficient for acquittal to show that the speed alleged by the officer is under the 85th percentile for the given conditions?


3)
Does it matter that this location is a de facto speed trap? No radar was used (AFAIK) so statutory speed trap laws don't apply. However, the Goulet opinion certainly suggests that de facto speed traps are not appropriate either. Goulet simply allows for police to spontaneously pace - which makes sense - but it still discourages simply substituting pacing technology for radar to sidestep speed trap protections for the accused.

4)
Are there implications at trial for doing my own speed survey that I may not be aware of? (Again, this link http://www.expertlaw.com/forums/showthread.php?t=117810 touches on the subject.

5)
As a legal matter, can I use discovery for the TBD?


Thanks,

Larry

[That Guy]

My question involves a traffic ticket from the state of: California (southern california)

I got a pacing 22350 ticket on surface streets. I am innocent. My core argument is that the speed I was going is "safe and prudent." The city's speed survey violates the MUTCD standards for speed surveys (among other problems) so the 85th percentile is skewed WAY too low; plus the survey was done in the middle of the week whereas I was ticketed on a Saturday morning when traffic is much lighter and prevailing speeds are much higher.

Doing my own survey (not as hard as you think) showed that my speed was below the 85th percentile for the conditions. Although I'm not a traffic engineer I have the technical credentials to conduct a survey that dramatically improved on the survey done by the city.

Questions:

1) What is the legal importance of an invalid prima facie speed limit in a pacing case?

From what I read, the only real effect is that it might technically shift the burden to the prosecution by removing the presumption of guilt. But, the officer admitted his judgment of safety was based on the speed limit alone (I was in the slow lane of a 4-lane road not passing anybody), so if the officer admits in court that his allegation of unsafe driving was based solely or primarily on the "invalid" prima facie limit, does this have weight? FWIW, the officer was CHP, and apparently not familiar with this city. I don't know why he was there.

2)

Is there a statutory, regulatory or other standard that establishes that the 85th percentile defines a "safe speed." This http://www.expertlaw.com/forums/showthread.php?t=117810 earlier thread says CalTrans defines the 85th percentile speed as safe, but I couldn't find it. Shouldn't it be sufficient for acquittal to show that the speed alleged by the officer is under the 85th percentile for the given conditions?


3)
Does it matter that this location is a de facto speed trap? No radar was used (AFAIK) so statutory speed trap laws don't apply. However, the Goulet opinion certainly suggests that de facto speed traps are not appropriate either. Goulet simply allows for police to spontaneously pace - which makes sense - but it still discourages simply substituting pacing technology for radar to sidestep speed trap protections for the accused.

4)
Are there implications at trial for doing my own speed survey that I may not be aware of? (Again, this link http://www.expertlaw.com/forums/showthread.php?t=117810 touches on the subject.

5)
As a legal matter, can I use discovery for the TBD?


Thanks,

Larry

Its pretty simple, really... If you were paced there is no survey requirement. One would look at the posted speed limit, and if your speed is higher, it becomes your burden to prove why/how your speed was safe.

While I do not know how you "conducted your own survey" rest assured it will have zero impact on the result, simply because when there is no law enforcement presence (a condition that is required for a valid survey) people may tend to drive at a speed that they are comfortable at, whereas if law enforcement is present, they are more likely to make a note of the posted speed and make an effort not to exceed it. You were driving with a CHP officer on your tail, I don't know for how long or how fast you were going... But did you drive at that speed thinking you could conduct your own survey and prove the existing one invalid, or did you drive at that speed because you were inattentive and didn't know he was back there?

That should answer 1 through 4; I don't know what you're asking in # 5!

[trafeng]

Larry,

I'm sure your brilliant, but there are many more factors that go into establishing a speed limit than just the 85th percentile speed. The only thing that the 85th percentile represents is the speed at which a majority of drivers are at or below.

As a curiosity, can you post your survey technique for us?

[flyingron]

Actually the 50th percentile speed has the majority of drivers at or below. I guess traffic engineers were excused from the statistics courses that the rest of us engineers had to take.

[That Guy]

^^^ LOL...

Traffic engineers are typically civil engineers, aren't they? And I doubt they are less smart than (I'm guessing) Mechanical Engineers, Ron! Or that their curriculum was less involved than yours!

There is obviously a good interpretation to the terminology that is used, and even more reasons why the 85th percentile speed is selected as the "preferred speed" or as the "safest speed"...

^^That *IS* actually *IT*^^...

(1) the 85th percentile speed is actually the speed that represent the upper bound of the preferred speed by the majority of drivers.

While it is a misnomer of sort, I'm sure you can deduce how that turns into "the 85th percentile represents is the speed at which a majority of drivers are at or below"...

(2) It also corresponds to the upper bounds of speed ranges where crash rates are at their lowest...

So it is THE SAFEST and MOST PREFERRED... What else could we ask for? (NOT a reduction!!!)

Its actually related in a way to the 50%ile speed you mentioned in that, for a normal bell distribution curve charting speeds, the 85th percentile is less that 1 standard deviation from the 50 percentile speed which is known as "the mean"!

[flyingron]

No I can't deduce that. Percentile is basic statistics. 50 percentile is the median. I.e., the point where half the samples (drivers in this case) are lower than that speed half are faster.
Majority, means more than half.
85% may be the preferred speed, or safest speed, or the speed the state finds acceptable.
Yes the majority of the drivers are at or below the 85th percentile speed, but they're also at or below the 51st percentile.

[That Guy]

No I can't deduce that.

Sorry to hear that!

Majority, means more than half.

85% is more than half! Its more that 15% too...

Yes the majority of the drivers are at or below the 85th percentile speed, but they're also at or below the 51st percentile.

Wait... It went up by 1%!

Is it usually higher on weekends?

Hell, now I can't deduce either!!!

[flyingron]

Don't you get started. His comments were wrong as stated. 85 is not "the point at which" the majority are traveling. It is the point where 85% are going that speed or below. I doubt seriously he's any sort of engineer. This is basic statistics that you have before you even start engineering courses.

[lbk]

Trafeng:

"I'm sure you're brilliant" sounds sarcastic, but perhaps I misunderstood you. I don't claim to be a traffic engineer; the job of conducting a traffic survey encompasses only a very narrow element of a traffic engineer's duties. The survey itself doesn't require a traffic engineer's expertise apparently since Huntington Beach is having the police do it for them: see http://articles.latimes.com/1994-04-...ntington-beach

It would be helpful if you shared some specifics about what part of conducting a speed survey require skills that only a traffic engineer possesses.

The law, as I understand it, is that (more or less) if I drive slower than 85% of the drivers under similar conditions, I am driving safely. Hence my question #2.

My methods, in brief, were simply to follow the MUTCD guidelines, ensuring free-flowing traffic. I only counted platoon cars that are selecting their own speed. If you have additional insights drawn from HCM or the green book, I particularly welcome your comments and suggestions.

Larry

- - - Updated - - -

That guy:

Thanks for the response. I see the home-grown survey as a straight-forward way to show that I was driving safely. While you disagree, I appreciate the thought that went into your response.

The CHP officer never rode the same speed as my car for any relevant length of time, so "pacing" to me meant that in a quarter mile a motorcycle started from 0 caught up to me and pulled me over. It's my understanding that the courts will accept "pacing" testimony based on essentially no time that the police actually goes the same speed as the violating vehicle so I downplayed the quality of the pace as an issue in the original post.

I saw the motorcycle approaching from behind me; there was very light traffic. I was driving in the slow lane, a safe distance behind a car. It didn't occur to me AT ALL, that I might be the target of the police: I was an hour early to where I was going and not in any sort of rush (yes, I know this is legally irrelevant). When I determined he was a police officer, I still had no inkling that he would be targeting me (because I know I wasn't speeding), so my first reaction was to ensure I was driving safely and to look for a place to pull over because I thought he was maybe trying to flag down the car ahead of me.

FWIW: if I know a police officer is present I make a conscious effort to ensure I do not exceed the speed limit.

[California student]

Trafeng:

"I'm sure you're brilliant" sounds sarcastic, but perhaps I misunderstood you. I don't claim to be a traffic engineer; the job of conducting a traffic survey encompasses only a very narrow element of a traffic engineer's duties. The survey itself doesn't require a traffic engineer's expertise apparently since Huntington Beach is having the police do it for them: see http://articles.latimes.com/1994-04-...ntington-beach

There's a difference between going out and collecting raw data at locations and in a manner dictated by an engineer and interpreting that information. There's a reason why lab techs aren't first authors in scientific papers despite often doing most of the grunt work.

My methods, in brief, were simply to follow the MUTCD guidelines, ensuring free-flowing traffic. I only counted platoon cars that are selecting their own speed. If you have additional insights drawn from HCM or the green book, I particularly welcome your comments and suggestions.

Just curious, how did you measure the speeds? Do you own a radar gun? When was the last time the radar gun was serviced and calibrated?

FWIW: if I know a police officer is present I make a conscious effort to ensure I do not exceed the speed limit.

I got a speeding ticket last July. I now make sure I go the speed limit regardless of whether or not the police are present. I figure if I'm going "too slow" on a freeway while going the speed limit that the People of the State of California can have their silly prize for playing a silly game.