Scenario regarding speeding charge - if a charge is not reduced at all at roadside, i.e. the charge, for example is "speeding 75 km/h in a 60 km/h zone contrary to s. 128," should that not mean the prosecution needs to prove that you are guilty of what you are being charged with, and not, simply, of speeding generally? I understand that if they prove a charge of even 61 km/h in a 60 km/h, they can obtain a conviction, however, if the charge itself in this case is 75 km/h in a 60 km/h - do they not have to prove you guilty of that offence in order to obtain a conviction?

Where I'm going with this is that even if the prosecution can prove an officer is properly trained and perfectly operates and the unit, conditions are optimal, and the device is properly tested and calibrated, there is still a margin of error of up to 2 km/h for any speed mesuring device, easily proved with the radar manual. So with that in hand, is it not impossible to prove the defendant guilty as charged, if the speed is not reduced by at least that amount?

Has anyone heard of this defence being tried? And certainly, if the prosecutor attempted to amend the charge in the middle of trial (by dropping the speed by 2km/h, for e.g.) there is case law to support this being prejudicial.

Thoughts?

mathers wrote:

there is still a margin of error of up to 2 km/h for any speed mesuring device

fyi, that is not accurate information

hwybear wrote:

mathers wrote:

there is still a margin of error of up to 2 km/h for any speed mesuring device

fyi, that is not accurate information

^^ depends on the speed measuring equipment being used^^

You can get your info on the margin of error after disclosure

fyi, that is not accurate information

Please enlighten on equipment in current use that advertises a degree of accuracy of greater than +/- 1 mph (1.6 km/h). thx.

If such does exist, the question remains open for all other equipment with accuracy of only +/- 1 mph (1.6 km/h) or worse. Defence ever attempted?

you are reading a USA manual if you see MPH and is not applicable to canada

it is in fact one unit of measure, whether it be km or mph

+/- 1 is that the unit can almost always will never obtain a reading of say 100.000000 etc km/hr

but the reading could be 100.9999999 etc (which is up to the +1) however the unit always will round down to the nearest whole number being "100", (which is the minus 1), thus the rounding down on every reading is a benefit to the driver

The info you have is for slightly older models and it used to be the norm, i.e +/- 1 MPH, or 2 KMH.... There are some models of moving radar that are capable of measuring speed as well as estimating distance to target. These units, due in large part to the calc'ns required offered a error margin of +/- 3.2 KMH, however according to my sources, these were not purchased by the respective police force for that very reason.

Add onto that the cosine angle effect which is always to the benefit of the target and you have a displayed speed on the radar which is always less than the targets actual speed.

you are reading a USA manual if you see MPH and is not applicable to canada

The unit is the unit. It will not be more or less accurate whether you are north or south of the border. 1 mph = 1.6 kmh. The accuracy is the accuracy, whatever it may be.

+/- 1 is that the unit can almost always will never obtain a reading of say 100.000000 etc km/hr

but the reading could be 100.9999999 etc (which is up to the +1) however the unit always will round down to the nearest whole number being "100", (which is the minus 1), thus the rounding down on every reading is a benefit to the driver

If the advertised accuracy of the unit is +/- 1 mph (or 1 kmh, for that matter), this is irrelevant to the argument. Yours is a discussion of rounding, not accuracy. If the reading is 100.1, it rounds down to 100, but due to the accuracy being +/- 1kmh, the actual speed could be 99.1 (or 98.5, if +/- 1.6).

mathers wrote:

you are reading a USA manual if you see MPH and is not applicable to canada

The unit is the unit. It will not be more or less accurate whether you are north or south of the border. 1 mph = 1.6 kmh. The accuracy is the accuracy, whatever it may be.

The accuracy is based on the unit of measure used and does not matter what type of unit is being used, it is the same math for each unit.

(ie: 7apples divided by 3apples = 2.33apples / 7 kph divide by 3kph = 2.33. kph / 7L divide by 3L = 2.33L / 7inches divide by 3inches = 2.33inches)

+/- 1 is that the unit can almost always will never obtain a reading of say 100.000000 etc km/hr

but the reading could be 100.9999999 etc (which is up to the +1) however the unit always will round down to the nearest whole number being "100", (which is the minus 1), thus the rounding down on every reading is a benefit to the driver

mathers wrote:

If the advertised accuracy of the unit is +/- 1 mph (or 1 kmh, for that matter), this is irrelevant to the argument. Yours is a discussion of rounding, not accuracy. If the reading is 100.1, it rounds down to 100, but due to the accuracy being +/- 1kmh, the actual speed could be 99.1 (or 98.5, if +/- 1.6).

I know the difference between accuracy and rounding and that is specifically taught on course and why it the unit is accurate WITHIN + / - 1kph on each displayed reading. Because it is next to impossible to ever have a reading bang on the exact precise number after the calculation with decimal places. So that is where the accuracy part comes in...the true/precise accurate speed could be the 100.1kph as you describe, however the unit does not display in 10ths, 100ths or 1000ths etc, so it automatically programmed to round down to the nearest whole number, which would be 100. So in this case the unit is accurate within 0.1kph.

The accuracy is based on the unit of measure

This is illogical. The accuracy of a device is not based on a unit of measure. The accuracy of a device is based on how accurately it measures something.

I know the difference between accuracy and rounding and that is specifically taught on course and why it the unit is accurate WITHIN + / - 1kph on each displayed reading. Because it is next to impossible to ever have a reading bang on the exact precise number after the calculation with decimal places. So that is where the accuracy part comes in...the true/precise accurate speed could be the 100.1kph as you describe, however the unit does not display in 10ths, 100ths or 1000ths etc, so it automatically programmed to round down to the nearest whole number, which would be 100. So in this case the unit is accurate within 0.1kph.

Your statements seem to imply that, but for rounding, any speed measuring device is 100% accurate, to a certain infinitesimal fraction of a kilometer. This is not however contained in the advertised accuracy of these devices. The devices are simply advertised as accurate to +/- x. That means that the internal reading itself, is accurate to within x. The internal speed clocked will never exactly represent the actual speed of the target. That speed will always vary to some degree from the internal reading. The advertised degree it can vary is x.

The radar is accurate to within +/- 0.1 km/h. However, as hwybear says, the radar cannot read 89.9 km/h, so it rounds down to 89 km/h in that case. And actually hwybear's statement about "accuracy being based on a unit of measure" comes directly from the radar manufacturer: Decatur's statement is the radar is "accurate to within +/-1 unit of measure," because anywhere from 89.0 to 89.9 km/h, it will read 89.

The radar is accurate to within +/- 0.1 km/h.

Thx Radar - we may now be starting to get somewhere. Is this information advertised in the manuals for all radar/lidar? And if yes, is it backed up with any independently verified empirical data?

The International Association of Chiefs of Police, among others, conduct field trials and audits on the devices for accuracy. This is independent of any tests that the manufacturer does to verify the accuracy of its products.

The information about the accuracy is advertised in the manuals.

Non-empirical, strictly anecdotal evidence: Every time I've been stopped the reading was +/- 1 km/h of the speed I thought I was doing, so in my experience the devices are fairly accurate. (Also I've been stopped often enough that I have a basis for this statement.)