How accurate are speed readings?

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Smileysmile

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I received a letter by the police today.
I'm alleged to have driven at 60 in a 50.
My MyDean hardwired dashcam recorded a speed of 71km/h to 76km/h over 1 min.

I downloaded the recording of the time I was alleged to have been speeding. The police mobile van I pass at 43 seconds in attached video.

Your thoughts please.

 
huh, interesting. Generally GPS devices are very accurate, even moreso than vehicle speedometers. It's interesting that your dashcam is reporting 71 km/h as you're passing the van (even faster as you approach), but they reported just 60.

I took a look at their website to learn a little more about their speed enforcement tools and it looks like they have a person shooting laser out the back window. Specifically, they're using a Kustom ProLaser III.

about-us-seatbelt-capture.jpg


It's hard to see the person in the dashcam video, but that van does have huge rear windows so it's a reasonable guess that they're doing something similar here. Rewatching your video, there was a decently long straightaway that they're shooting down and so cosine error wouldn't be a factor. Like you said, you were doing 71-76 kph throughout the range they could target you.

Perhaps they just wrote you for a lower speed on the citation? I've seen officers do that here in the US if you're friendly, for example, but I'm not really familiar with to what degree that's done for tickets in the mail like this.
 
Smileysmile said:
I'm alleged to have driven at 60 in a 50.
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I assume that is in MPH?

So you were doing about 46MPH, which would be legal.

As Vortex suggests, when you are doing a constant speed like that, the reading is likely to be within +/- 1km/h.

If you are rapidly changing speed, or cornering then they can be a fair way off at times, or even a long way off, but not in that situation.

I would challenge that ticket, submit a frame from the video and make it clear that you have a full video and ask for a copy of their evidence, which you should check carefully. The time is on your video, the speed is on it, so there is reasonable doubt about their reading. Legally, they have the better evidence, but I would expect it to be dropped without needing to go to court.
 
You have a minute of nearly constant speed there, if you go to Google Maps, use the Measure Distance function to measure the distance traveled in miles, multiply by 60, you then have the average speed over that minute in mph, very accurate and independent to the GPS speed. I would expect it to match the GPS. You can submit that as extra evidence against the "police" reading. Very hard to argue against that when theirs appears to be so far off. With those two pieces of evidence, you would very likely win in court, but they wont take it that far.
 
Ah is it in MPH? Sorry info got confused with the mix of MPH and KPH.

As for bringing dashcam footage to court, IANAL and I don’t know how similar your laws are to ours here in the US, but I’m not sure if dashcam speeds are admissible as evidence in court.

For example, because people are constantly going to try and challenge the alleged speeds in court, officers have to jump through a bunch of hoops to have their equipment tested and verified. For example, they’ll need to have their equipment sent in for recertification periodically, for example once a year, and then they often need to do daily tests to further verify that their equipment is operating properly. Some even require officers to do it both at the beginning and end of every shift. Then those reports all need to be documented. Furthermore officers will need to go to court and testify about how sure they were that your car was definitely the one being targeted. For example, were they accidentally targeting the car next to you or behind you? The farther away the target is, the smaller it is, plus the more the laser beam’s divergence becomes a factor (aka the beam gets bigger and thus it’s easier to pick up an unintended target). For this reason some places actually limit how far away officers are allowed to shoot laser. Some guns even let you set max distance limits so they won’t work beyond certain distances.

All this is to say there’s a lot that goes into verification of the speeds on the tickets, but incorrectly issued tickets can and do happen for many reasons. This is where the advice usually turns into “get a lawyer” because they know all these ins and outs, they’ll know if the dashcam’s GPS footage is admissible as evidence, and they may even be friends with the judge and know the best ways to get your ticket reduced or dismissed.
 
Vortex Radar said:
As for bringing dashcam footage to court, IANAL and I don’t know how similar your laws are to ours here in the US, but I’m not sure if dashcam speeds are admissible as evidence in court.
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In a British court, generally all evidence is admissible.
The question is if there is reasonable doubt that the police evidence is accurate, and I think in this case there is.
The police have to prove their case, the defendant just needs to provide reasonable doubt.
The person with the laser gun isn't actually police anyway, so it is their word and video against your word and video, and if their video shows the same as this video, they will check it before actually going to court and drop the case.
I don't think any lawyers are required, unless it is really important not to lose. The penalty on losing is going to be a lot less than the cost of the lawyers!

Smileysmile said:
Your thoughts please.
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Let us know what happens, we don't see many videos like this, and in most cases the speed gun was probably accurate!
I suspect an appeal will get it dropped very easily...
If it does go to court, it would be a quick visit to the magistrates court, nothing to worry about.

Do check the speed with Google Maps first though... or give us the location, so that someone here can work it out...
 
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Nigel said:
or give us the location, so that someone here can work it out...
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I got 71.4 Km/h or 44.4 mph average, so I am happy to believe your GPS saying that you never went above 47 mph.
 
I have never tried with dashcams as the speed is not easy to see on the little screen, but i have for years gone by the speed on my phone, and gone past speed traps at the listed MAX speed, and NOT gotten fined.
Mind you here police also deduct i think its 4 km/h to account for any inaccuracy in their equipment, but then the hammer also fall, for instance my friend got fined for driving 51 km/h in a 50 Zone ( they probably measured him to do 55 )

No one will rule on a dashcam reading, but the video dokumentation where you can determine how long time it took you to drive from "A" to "B" is valid, and then you just need to measure the distance between those 2 points, add a little math, and you have your exact speed.

My friend back when he was a motorcycle driver, he once got measured going fast in town, and he also felt it was unreasonable fast so he was moaning about it, so while bickering with the cops the one operating the equipment ( must have been a radar gun back then ) he came over and said " we better forget his speed CUZ i just measured a mother with a stroller to do 40 km/h "

These days i think COPS do a calibration / check of their laser gun when they leave the station.
 
kamkar said:
These days i think COPS do a calibration / check of their laser gun when they leave the station.
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I think it is quite easily take bad readings with a calibrated laser gun, but with a clear road, and car coming straight towards the van, it seems surprising in this case, and I would have expected them to notice that the car was going relatively slowly using their eyes and ears!

Possibly they got the wrong car, but that should be shown on their evidence images/video, and Smiley admits he was there.

So, a bit surprising, but having checked the GPS speed via google maps, it is the speed gun that is wrong, or its operator is making up false reports!

P.S. If the true speed was 46, the speedometer likely read 49/50, so Smiley was driving as expected in a 50 limit.
 
Cops here have gotten new hardware, now their laser guns also record video or is it take a photo.
Gear in ATK vans also updated, it is now WIFI so they can put the camera / laser unit anywhere in relation to the van, and i have seen that a dew weeks ago where the van was in one place and the cameras was on the other side of the road aiming in my direction.

Also the H&K MP5 they had for years ( and as i think had problems with for unknown reasons ) well they will soon get the SIG MCX to replace those

I just wonder why, it is not like they use them,,,, like pretty much ever, police here aught to shoot a guy at least every week, as there are plenty of dangerous people here to deal with.
 
Today I received this. If anybody has been following my thread.

Alleged 60mph in 50mph.

I enclosed a brief letter stating I had a dashcam and the video clip said I was travelling less than 50. Great news but what changed their mind to pursue.

I have attached their letter.
 

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Smileysmile said:
Great news but what changed their mind to pursue.
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They checked their own video, and it agreed with yours!

Something I think they should have done before issuing the ticket, thus they can claim an administrative error, because they didn't check.

I guess there was a bad laser gun reading which started the process of issuing a ticket, no idea if they actually check all their videos before issuing tickets, but I suspect that letter is a bit of a lie and they never actually checked their evidence before issuing your previous letter. We don't see many of these cases though, so maybe it really was an administrative error of some sort. I still find it a bit surprising that the person with the gun didn't realise that you were nowhere near fast enough for a ticket, maybe he just pressed a wrong button somewhere and accidentally triggered an automated ticket.

Thanks for posting the update, always good to hear the outcome, might be useful for next time someone has the same issue.

You can have a good night's sleep now!
 
mentadent said:
Do a FOI request to find out why
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You can't do that for personal data, which I think is what we want to see, so you would need a data protection act request for your personal data; but since they have already stated that all his personal data has been removed from their system, presumably including all the video evidence, I doubt that there is anything of interest left to be requested! Their letter was carefully worded to get them out of any potential trouble!
 
Smileysmile said:
I think my brief letter explaining I had a dashcam and it's reading was under 50.
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I'm fairly sure they wouldn't accept your word on that, they would have checked their own video and found that you were correct. I think they need their video to show you speeding before they can expect to win a court case, even if you didn't have a dashcam. Laser gun evidence on its own is always questionable, it is always possible to get some false readings, even though they are normally pretty accurate. That's why we have these camera vans with lasers and video cameras instead of just a police officer with a speed gun at the side of the road.

Without the dashcam, you wouldn't have known that it was worth fighting the ticket, so yes, the dashcam has paid for itself.
 
Excellent result.

Had the circumstances been different and I'm not sure if the laws in Wales are the same in England, but if your licence was clean at the time of the ticket and at the speeds they claim you were going, you would automatically qualify for a "Speed Awareness Course" providing you hadn't done one in 3 years, via Zoom from your home.
I had my third National Speed Awareness Course in 10 years, 2 months ago.

Source for speeds info: https://www.police.uk/advice/advice...d-a-speed-camera-activation-letter-or-notice/
 
GPS recording of speed will easily overturn a speeding conviction.
 
Aph said:
I'm not sure if the laws in Wales are the same in England
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The law should be, but I think the decision on courses depends on which police force you are in rather than which country, some forces are a lot keener on courses than others, and it would still have cost £88 for the course, you only avoid the points.
 
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