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I need help to figure out something on a recent speeding ticket I got here in California.

In the "Location" box where the cop is supposed to indicate the approximate location of the violation, such as street name, intersection, highway etc. the cop put this "+390 - Laser".
I called the police department and the person who ansered the phone had no idea what that meant! I suppose it means something but that person didn't know. I also tried to google it. Nothing came up.

The cop used a laser gun, and indicated 56mph in a posted 30mph area on the ticket. I know how laser guns work, they need a reflective flat surface etc., how accurate is a laser gun used on a motorcycle ?

Thanks.

When I wrote those I used +390 to indicate the violator's vehicle was 390 feet from my location when I first received the violator's speed. Another distance is locked in when you release the Lidar's trigger and I'd commonly note that on my copy for court testimony. The + indicates the violator was approaching my location as opposed to receding. I'd image this police officer was using similar info. I always wrote PL123 or similar to indicate I was using our ProLaser Lidar with 123 representing the serial number of the unit.

In my experience and testing, extremely accurate. It is aimed like a rifle, unlike a Radar which is "aimed" more like a lawn sprinkler. A motorcycle headlight's reflector presents an excellent target for the Lidar.

Sorry he tagged you.

Bud,
Thank you for clarifying that for me.

budH wrote: In my experience and testing, extremely accurate. It is aimed like a rifle, unlike a Radar which is "aimed" more like a lawn sprinkler. A motorcycle headlight's reflector presents an excellent target for the Lidar.

It must be accurate in lab testing conditions, I have no doubt.
What I need is the error that accounts for handling by a human on a moving vehicle at a distance.
In my case, I was cited at 56mph, which is 26mph above the posted speed limit. In california, that removes the option to do traffic school, and cause points on the driver license, hike the insurance rate etc.
I am going to trial for this one, and I need to show that the measurement was within the error range, which hopefully will make the judge give me traffic school.

390 ft sound like a huge distance.
If he was aiming at the headlight, say 10" in diam, at 390 ft, he was working within less than 3 deg angle, equivalent to holding the cross hair on a $0.25 coin at a distance of 39 ft.
I may bring one of those (red) laser pointers to the court room and have him shine it on a dime placed at 39 ft and see he can hold it steady

BTW: Here's an report on speed cameras and laser guns checked in real life conditions: see the slip effect part !!
http://www.bbc.co.uk/insideout/south/se ... eras.shtml

Not only was the infraction 26mph above the posted limit, you were tagged for going nearly 90% over the limit! If that's closer to the normal flow, then I think the road is due for a more realistic posting.

Otherwise, count your lucky stars you're riding a slow Bavarian sporty bike!

Sorry not a LEO or any expert on laser/radar guns but...

1. Love you're idea of the quarter and a laser pointer. I think you got a great argument there for the"human" factor giving a possibly misdleading reading.

2. You said you were CITED for doing 56 ina 30 zone...How fast were you really going???? Inquiring minds wanna know....

Craig

rph802 wrote:How fast were you really going???? Inquiring minds wanna know....

Oh! come on, it was a speed trap!! A long stretch of down hill, one wide lane coming out of a canyon. You'd have to press the brakes real hard to stay close the posted speed limit.

The funny thing is that road is usually a parking lot, which was one of the reasons I am using a motorcycle to commute to work. Anyhow, it was two days before Christmas, a perfectly sunny solcal day, people had already taken off for the hollidays. So, of course the police know there won't be much traffic on that road and people could finally be moving... They came to collect!

The Judge (or magistrate) will not even entertain your laser pen demonstration. It is not even close to the size and weight of the LIDAR gun. The accuracy of the LIDAR is +/- 1 mph and is accurate at distances up to and over 5,000 feet. Beating a ticket from a LIDAR gun is basically impossible. You would have a much better chance of beeting a ticket from a radar. A radar does not have pin point accuracy like a LIDAR does.

Speed kills!

Speed kills!

Boy oh boy, you sure have your non thinking lock step talking points down pat.

It would be more accurate to say something like idiot drivers kill or drunk drivers kill, but speed in itself in no way kills.

Try being a State Trooper for a month and then tell me that speed doesn't kill. I was trying to be helpful and I get slamed? Thanks for the support SHIPMATE! That will teach me to post.

Dominor wrote:The accuracy of the LIDAR is +/- 1 mph

YEEEES. That's what I was looking for. Do you have any reference to that number. I need to show something to the judge.
See, at 56mph, I don't get a chance to do traffic school, so I get points on my driver license. If 56 mph, +/- 1, that puts my speed within the error range. I guess depending on the judge, she will keep the fine but allow traffic school. We will see.

Dominor wrote: and is accurate at distances up to and over 5,000 feet.

Again, that's lab-environment testing. How about a person holding the gun. What is the error rate ? Especially, that the person does not have visual feedback e.g. a visible laser, all he relies on is the crosshair.
How doing it on a motorcycle that has a smaller reflecting surface than a car.

Dominor wrote: Speed kills!

Funny you say that, because that was exactly the first thing the officer said when he stopped me. And I replied "I agree, on a motorcycle you are in danger at ANY speed. As a matter of fact a motorcycle going slower than traffic speed is in more danger than going at a slightly higher speed." He noded.

dragonmojo wrote:Not only was If that's closer to the normal flow, then I think the road is due for a more realistic posting.

Two issues here. As far as the second, I'm donning my fireproof undies as I type.

Dragon (in a past life I was a highway engineer, still play one on TV):

You cite one factor for posting a speed limit. It's certainly not the only, nor typically the dominant one. There's the type of area (residential with lots of driveways) the geometry of the road (both horizontal and verticle sight distances), even accident history, public complaints, facilities (school zones are an obvious one) and others.

If speed limits were only based on what the traffic was flowing at, I suspect Show Low, Az would print all their signs with three digits.
- - - - - - - - - - - -
And now for the bomb throwing......

Guys, my late brother-in-law (look up the phrase "real man" - not macho, but "real" - in the dictionary and see Ray's picture) was a trooper, and our oldest boy is currently a trooper. My wife heads (the Alabama Division of) the Federal agency responsible for trucking safety. Me, I'm a dumb old civil engineer, but I've read hundreds of accident reports and investigated fatal accident sites to see if the road contributed. Try watching various body parts being removed from wreckage, especially kids. Time after time after time. It gains you a whole new perspective. One you might disagree with, but not one that should be trashed.

Now, do I think the "Hoon" is safer at 110 on his R1200ST on roads he knows than Granny Smith with a cell phone in her ear, applying lipstick at 70 mph in her 1984 Buick using the original shocks? Of course I do.

But that's apples and oranges, guys. Be honest. Given even the expert riders on here (and I bow in my unworthiness)....are the margins for error not less at 100 than 75? Known any pretty good riders who have died and then heard it said that, "He got in over his head."? Don't you have a longer stopping distance at high speed? How about reaction time/distance travelled when that deer darts in front of you? The same at 75 as 100? The rare mechanical error occuring at 100 versus 75? It seems I read a post about ABS causing lockup on ripples at 130-140 the other day. Would that pucker factor have been as great at 80? Would the lock up even have occurred?

Drugs kill, booze kills, lousy equipment kills, sleep deprived drivers kill, poor roads kill and, yes, speed kills. Sure it's more complicated than that. Sure, "Speed kills" is shorthand. But there's certainly some truth in the shorthand. And I think the reaction to Dominor was a bit harsh.

Time to "stop, drop and roll", I guess.

Popgazer.

Try DOT HS 809 811 (NHTSA)

(Way too much pasted below - I added the "bold". From NHTSA - first - and the Transportation Research Board - last. The "meat" is nearer the end. Hope it helps.)

Section 1 - General Information

1.1 Scope
This module is limited in scope to laser speed-measuring devices and systems used by law enforcement agencies to enforce vehicle speed regulations. It applies to devices that comply with FDA Class 1 eye safety regulations (§ 2.2.3).

1.2 Purpose
The purpose of this module is to specify minimum performance specifications and test procedures for lidar devices used by law enforcement agencies to enforce vehicle speed regulations.

1.3 Application
This document applies to laser speed-measuring devices and systems that transmit coherent infra-red light pulses, measure the time of flight for the pulses reflected from moving vehicles, then calculate and display or output the speed of the target vehicle, and may automatically record images of those vehicles which exceed a preset speed.

1.4 Definitions

1.4.1 Accuracy - the degree to which the lidar device measures and displays the speed of a vehicle.

1.4.8 Cosine Angle Effect - the discrepancy between the target vehicle's speed along its path and the closing speed measured by the device.

1.4.9 Display - a visual readout device.

1.4.10 Erroneous Reading - an incorrect target speed displayed by the lidar device that is not due to a target vehicle, or which is not within the required accuracy tolerance of a target vehicle's speed after accounting for the cosine angle effect.

1.4.11 Functional Beamwidth - the angular range over which a small, stationary retro reflective target can be detected against a background of sky or distant scenery.

1.4.28 Target Discrimination - the ability of a speed-measuring device to differentiate between target vehicles.

1.4.29 Target Speed - the speed of the target vehicle along its path, with respect to the ground.

1.4.31 Target Vehicle - the vehicle at which the lidar unit is aimed using the unit’s visual sighting device.

1.5 Units of Measure

This document is a specification for practical measuring devices of comparatively low precision. We have attempted to develop specifications that are practical, whether the UUT reads in kilometers per hour (km/h) and meters (m), or miles per hour (mph) and feet (ft). The speed accuracy requirement as stated below is +2 km/h, -3 km/h (+1 mph, -2 mph). Direct conversion from km/h to mph would give a tolerance band of +1.24 mph, -1.86 mph. Practical lidar devices read to integer precision only, so some decision must be made in order to give the tolerances in integers.
The same spirit of practicality is carried over into other measurements. For instance, to check a lidar device's distance measurement function, two somewhat arbitrary baselines are needed, as specified in §2.4.1. One baseline shall be in the range of 6 m (20 ft) to 30 m (100 ft), and the other shall be at least 90 m (300 ft). Again, the conversions are not exact.

In the simulator software, the settings for the primary system of units are those that are appropriate for the UUT. These determine the ranges and units of most inputs and outputs. Again, some liberty was taken in rounding the range limits. The presence of round-off discrepancies should not motivate sloppy measurement. When the actual baseline is set up, it should be measured by surveying methods to an accuracy of 1 cm or better. Also, if the measured baseline is, for instance, 90 m (295.28 ft), a traditional-units lidar device should be moved forward 0.28 ft from the fiduciary mark, so that it is presented with a less ambiguous measurement task.

Section 2 – Requirements

2.4 Range Accuracy

For a baseline distance between 6 m (20 ft) to 30 m (100 ft) and for a baseline distance at least 90 m (300 ft), the target range reading shall be correct to within ± 0.3 m (±1 ft).

2.5 Long Range

The lidar unit shall be capable of measuring distances of at least 300 m (1000 ft).

2.6 Beam Characteristics

2.6.3 Target Discrimination. The functional beamwidth of the lidar unit shall not exceed 5 mrad as tested in accordance with §5.6.3.

2.10.6 Audio Tones and Error Messages. If the lidar unit emits audio tones which vary under conditions of valid and invalid data, then the relationship of the sounds to the displayed reading shall be consistent (§5.10.6).

2.11 Speed Accuracy: Laboratory Simulation

For simulated speeds of 16 km/h to 320 km/h (10 mph to 200 mph), each lidar unit shall display the speed to within +2 km/h, -3 km/h (+1 mph, -2 mph). For speed accuracy requirements for field operation, see §2.15.

2.11.1 Smoothly Moving Target. When tested on the simulator in accordance with §5.11.1 at twenty or more combinations of speed and distance which are within its working range, the lidar unit shall give no erroneous speed readings. A blank display is not in itself an erroneous reading, but trials that give a blank display or an error message shall be repeated, and the unit shall ultimately give an accurate speed reading at every setting tried. There is no requirement on the range reading in this test.


2.15 Speed Accuracy: Field Operation

When tested in accordance with §5.15, the lidar UUT must display the speed of a target vehicle within +2, -3 km/h (+1, -2 mph).
2.16 Vehicle Determination

-------------------------------

From the Transportation Research Board:

Title: COMPARISON OF PORTABLE SPEED MEASUREMENT DEVICES
Accession Number: 00978591
Record Type: Component
Language 1: English
Abstract: The accuracy and precision of five common portable speed measurement systems were evaluated in a controlled field evaluation. The following systems were evaluated: traffic classifier with pneumatic tubes, traffic classifier with piezoelectric sensors, tape switches, radar, and lidar (i.e., police laser). A test vehicle with a calibrated Nitestar distance-measuring instrument (DMI) made 100 passes through the test site at two speed levels (50 passes at 55 mph, 50 passes at 35 mph), and speed was recorded by each device for each pass. DMI speed was deemed the true speed for each pass, and deviations from the DMI speed for a given device were considered errors. Paired t-tests were performed on the speed data measured by each device versus the DMI. The following conclusions were drawn: (a) All devices performed equally well for the 35-mph trials. (b) Lidar and radar were the most accurate and precise devices for the 55-mph trials. (c) For all devices, any errors that occurred for a single speed measurement were relatively small (less than +/- 1.5 mph). (d) With the exception of radar, all devices were slightly less accurate and less precise at higher speeds. (e) There was little difference in performance between on-pavement devices (i.e., tubes, piezoelectric sensors, and tape switches). (f) Inaccuracies observed in on-pavement equipment likely were caused by slight measurement errors during placement of the sensors or movement of the sensors resulting from repeated tire hits. Because all devices were relatively accurate, the researchers recommended that portable speed measurement equipment be selected to suit the characteristics of a given data collection situation.
Supplemental Notes: This paper appears in Transportation Research Record No. 1870, Data and Information Technology.
TRIS Files: HRIS
Pagination: p. 139-146
Authors: Gates, T J; Schrock, S D; Bonneson, J A
Features: Figures (5); Photos (3); References (3); Tables (5)

Monograph Title: DATA AND INFORMATION TECHNOLOGY
Monograph Accession Number: 00978573
Corporate Authors: Transportation Research Board
500 Fifth Street, NW
Washington, DC 20001 USA


Availability: Transportation Research Board Business Office
500 Fifth Street, NW
Washington, DC 20001 USA
Order URL: http://trb.org/news/blurb_detail.asp?id=4405

ISBN: 030909464X
Publication Date: 2004
Serial: Transportation Research Record
Issue Number: 1870
Publisher: Transportation Research Board
ISSN: 0361-1981


Index Terms: Accuracy; Distance measuring equipment; Errors; Field tests; Laser radar; Performance; Portable equipment; Precision; Radar; Speed data; Speed measurement; T test; Tape switches; Traffic classifiers with piezoelectric sensors; Traffic classifiers with pneumatic tubes
Subject Areas: H55 TRAFFIC FLOW, CAPACITY AND MEASUREMENTS
I72 Traffic and transport planning

Popgaser,

There is a traffic ticket attorney in LA that beats more than 95 percent of tickets. I think his name is Sherman & his office is in Sherman Oaks. (Sherman from Sherman Oaks) Google "Traffic Attorneys" "Sherman Oaks" & I think he comes up. Costs $2500 for his assistant & $3500 for him. Depends on how big your insurnce hit could be. If you use him you don't even go to court.

For Dominor (with apologies to popgazer for the hijack):

Please don't take it personal. As a member of LE, you would have a lot to contribute to this forum. You have to understand, some of our members enjoy riding at, shall we say, slightly elevated speeds.

Although most of us have not met Dean (and probably most of us would like to), by all accounts he is a great fellow and a highly accomplished rider. I think the point is that speeding alone is less of a factor for skilled riders than incompetent drivers doing stupid things. I have riding friends who can probably match him in skill and whom leave me behind routinely.

On the other hand, as JCsman pointed out, reaction times even for skilled riders, need to take into account stupid drivers and road conditions. It's just that some of us have better reactions than others!

My son is a volunteer fireman and EMT and would concur with your opinion that speed, especially accompanied with little skill, will kill. As a father to two teen-aged drivers, I preach the same message.

Please stick around and join the discussion. I occationally ride with a State Trooper on a Ninja. It is interesting. He won't do certain things but admittedly will speed some under the right conditions. Of course, he probably can get out of a ticket also.

Now back to your regular thread!

Dominor, please accept my apology for my knee jerk reaction to "Speed Kills". IMHO the issue is much more complex as has been pointed out by both wncbmw and JCsman above. Both bring up excellent and valid points. I just react to any one who makes the statement "speed kills" and nothing else.. If no one ever exceeded 30 MPH on any road or highway, traffic carnage would approach 0. However on the other hand, if wreckless driving, driving while impared, and unskilled drivers were eliminated, the rate of carnage would drastically drop as well. On a clear clean low traffic, excellent visibility country roadway when a state trouper stops a "speeder" he is doing nothing more than money generation and allowing his Meaglomenia to come to the fore front, (don't call "speeding" in those cases wreckless driving), and you have to admit that it is fun being the hunter hunting the hunted.

On the issue of driving or riding fast in a crowded area, town, school zones etc, speeding not approiate in the least.

It was trial day today. Here's an update.
The officer is no longer with the police department; he didn't show up to at the court today; case dimissed; I get a refund of my bail and that's it.

Thank you all for your contribution. I went prepared for the trial.
I learned alot about speed surveys, laser guns and the working of police department etc. So overall it was a fruitful experience.

For anyone who is thinking of fighting a ticket, do it. It is at least a good learning opportunity.

More importantly BE VERY COURTEOUS and FRIENDLY with the cop. After he stopped me we had a nice chat about BMW motorcycles (he was riding one), ABS, riding experience etc. Before we departed we had a friendly hand shake. He was almost insisting that I should present the ticket to the court and see if it can be thrown out What I discovered later is that he had altered the ticket (wrote the address in the wrong line) after he had handed me my (CARBON) copy and did not notify the PD to issue a correction!
That alone could have been enough to have the judge throw out the citation.

Thanks JCman, I went through DOT HS 809 811 (NHTSA) documents. It seems that everything is geared toward tagging automobiles. There's no mention throughtout the entire document of motorcycle.

Here's an interesting thing (see figure below): the target used for testing lidars is 300 mm Horiz/width by 150 mm vetical/height.
There's no flat reflective surface on the front or back of the motorcycle that matches that size. The head light is smaller than 300mm.
I don't know what's such an argument is worth, I didn't get a chance to present it, of course!

popgazer,

Glad you got it dismissed. I'm sure you were being attentive - just trying to get out in front of all those SUV's!

In Delaware, we're not required to know the inner-workings of the LIDARs - just how to use them. As a prior ProLaser LIDAR instructor, I do know more about them than some. It's been a while, but I believe at 4000 feet, the laser beam is approximately 2 feet wide. You can tell instantly that you are targeting the vehicle you have sighted because you track that vehicle for a few seconds, receiving audible and visual cues that you are locked on to one particular vehicle. You can just follow said vehicle even if it weaves through heavy traffic. It's like shooting fish in a barrel - very easy. Trooper-proof even! 390 feet is not a far LIDAR shot for a user with a steady hand - even for a motorcycle. Yes, the headlight reflector is the best target but helmets, motors, and instrument pods all work. I'm certain I could make you a believer in about 10 minutes of testing out a ProLaser LIDAR. When we first got them about 15 years ago, we demo'ed them for several magistrates - allowed them to "shoot" some traffic. All were very impressed. Plus, the new ProLasers are even better - locking on very quickly and I believe they have even better range.

RADAR? Well, that's a different story entirely... Although they have also improved over the years.

budH wrote: I believe at 4000 feet, the laser beam is approximately 2 feet wide. You can tell instantly that you are targeting the vehicle you have sighted because you track that vehicle for a few seconds, receiving audible and visual cues that you are locked on to one particular vehicle. You can just follow said vehicle even if it weaves through heavy traffic.

I agree that laser guns make VERY accurate measurement on anything big that has a exposed flat surface!
The assumption always made is that the reading is done twice on the same spot, or on two spots at the same distance.

Just as a reminder, laser guns work as follow: laser guns are good at mesuring distance ONLY. This is achieved by sending a laser pulse (90 nm wavelength) and measuring the time for the pulse to to travel to a reflective surface and back. Having the speed of light and that measured time the gun computes the distance travelled. By repeating the measurement as a fixed time (I believe it is usually 0.3 sec) the laser gun measures a first distance, then repeats the mesaurement 0.3 sec later. The difference between measurement is assumed to be the distance travelled by the target vehicle. So for example, if a vehicle is traveling at 45 mph, then the vehicle should have travelled 6.19 m (51.6 ft).

390 feet is not a far LIDAR shot for a user with a steady hand - even for a motorcycle.

Steady hand. That's it! Let's consider the 390 ft, the headlight measures about 8 inches, and the beam is expected to measure 4" due to the spreading. The virtual target zone is then 12" wide (1 ft). The officer must be steady to within 1/390 radians angle (0.07 Deg). With no tripod it seems extremely hard to be this accurate !!

What happens in most cases is that beam wonders around by a foot or 2. If you are aiming at a flat surface, things don't change significatly.

But consider the following:

Let's consider a motorcycle coming toward an officer who is holding a laser gun. The officer presses the button when aiming at the headlight. The hand movement never stops. It is likely to wonder off of the deadlight. In effect. what is likely to happen is that the first pulse reflects off of the headlight, but the second one is likely to reflect off of something else, helmet, engine, tank sides etc. Let's say the helmet, that's 1 ft above the headlight, but 3 ft behind it.
At vehicle speed of 45 mph, the expected distance travelled is 51.56 inches during the 0.3 sec inter-pulse interval. However, because of the slippage (hand movement) the measured distance is going be 51.56+3=54.56 ft. This puts the vehicle at 51.56 mph. If the posted speed is 40 mph the officer may let you go at 45 mph, but not at 51 mph.

Laser guns are impressive, because they seem to lock on a target and give what seems to be an accurate reading.

I wonder what kind of results you would get if you have 2 or more people reading the speed of a motorcycle at same time !!!
See, that would establish a good error baseline.

You are correct of course. All a LIDAR does is measure distance and calculates distance changes over time via incredibly rapid laser pulses. Simple in theory - thanks to the wonders of electronics, relatively simple in execution.

Aiming, for the ProLaser anyway, isn't difficult. As I posted previously, the cues given by the electronic sight and audible tones verify that your aim is true.

I remember the ProLaser has built in software that discounts distance changes that are out or range over a short period of time - for instance, reading a car headlight, jumping to the roof, and then back to the headlight again. With very short distance changes, as between a headlight and a helmet, that may or may not be filtered out as an error condition - it would depend if the distance change was unreasonable. I'd have to dig out my ProLaser manual to give specifics.

Again, if you're ever in Delaware, I'll let you test drive one so you can possibly reconsider your opinion.

Unfortunately, this will all be a moot point in the future when common use of newer speed measurement technology is adopted - such as http://www.its.washington.edu/pubs/Auto ... IV05-2.pdf

budH

Thanks for sharing your knowledge and experience.

I was wondering about something that I would like your opinion on. With the proliferation of EZ Pass electronic toll devices, do you think that states will ever use them to assess speeding fines? It would be pretty simple to calculate that a driver got on the NJ turnpike at 10:00 AM at interchange X and exited at 11:00 AM at interchange Y, so his average speed was 76 mph, which is 11 mph over the limit.