Dashcam Vs Speed Gun

[PeteTheGreek]

Anyone ever been in a speeding scenario? Pulled over by a cop who said you were over the speed limit, but your Dashcam said otherwise?
What's the accuracy of a Dashcam Vs that of a Gatso or other speed trap?
Where would you stand in court?

 

[Nigel]

In the UK, I don't think you have any chance against a speed camera, although it is worth checking the camera's photo evidence if you think it is wrong. You might have some chance against a laser gun since they can be used incorrectly, and probably have no chance against a police car, which would have its own video evidence that is better than yours, so it is unlikely that they are wrong.

The dashcam GPS is very accurate as long as you are going at a constant speed, any heavy braking or acceleration and your GPS evidence is useless. Unfortunately the GPS can't reliably indicate when you were braking/accelerating, which makes all the GPS evidence pretty useless in court, even though it is a good guide to when it is worth fighting a case.

The dashcam video evidence is also very accurate, and accuracy is not affected by braking/acceleration, so if you do some forensic analysis of your video frames then you do have very good evidence for fighting a speeding case, but it is evidence of the truth, so don't bother unless you really have been incorrectly charged!

 

[DT MI]

Consumer dash cams and their GPS units are uncalibrated and uncertified, unlike official speed monitoring devices. On that alone (discounting analysis of the video itself or other evidence) on a head-to-head basis in court the dash cam will lose.

 

[kamkar]

Yeah the Gatso camera will always win, unless your video itself can do something, the GPS in dashcams i only see as a gimmick, even if it is one i like to have.

Even the official speed cameras here, i still think they have to deduct a few KMH to account for a possible inaccuracy in the camera, even if it is official and all, i also think it is the same with a cop using a laser gun, or the predominant ATC cars that are used here,,,, which i also think use a laser to determine speed.

My M8 was measured to do 55 kmh in a 50 kmh town zone, they then deducted 4 kmh for inaccuracy so my friend got fined for doing 51 in a 50 zone. Which is the same fine if he had been going 65 kmh.

 

[PeteTheGreek]

Yeah the Gatso camera will always win, unless your video itself can do something, the GPS in dashcams i only see as a gimmick, even if it is one i like to have.

Even the official speed cameras here, i still think they have to deduct a few KMH to account for a possible inaccuracy in the camera, even if it is official and all, i also think it is the same with a cop using a laser gun, or the predominant ATC cars that are used here,,,, which i also think use a laser to determine speed.

My M8 was measured to do 55 kmh in a 50 kmh town zone, they then deducted 4 kmh for inaccuracy so my friend got fined for doing 51 in a 50 zone. Which is the same fine if he had been going 65 kmh.

That's what you call zero tolerance. That's extreme policing. Terrible.

 

[Kremmen]

A friend of mine got fined for doing 71mph in a 70mph zone under similar circumstances. He opted for an expensive one day road safety course instead of a direct fine and licence points.

On our UK motorways we are seeing the latest HADECS3 cameras. These cameras are super accurate. They are the ones that are on a gantry shelf on the side of the motorway and not the traditional overhead type. They are also variable so if the speed limit changes due to traffic ahead, so does the camera.

At the time, the normal car speedo calibration was about a 6% to 10% overread, by law, so when he was caught the letter said his speedo must have been reading over 75mph so no defence.

However, this 6% to 10% overread is now reduced in new EU cars from 2021, again, by law, as they now have safety systems that can read roadside speed signs and automatically react. My new car has such a system, if I choose to activate it, which I don't. I also noticed the far more accurate speedo.

My 2007 Honda Civic speedo was well out, at GPS 70 it was reading 77
My 2009 Civic was slightly better and read 75
My 2013 Civic read 74
My new Honda Jazz, at GPS 70 reads 71mph.

My GPS figure agrees on my Garmin DS61, my Viofo dashcam and phone speedcam app.

 

[PeteTheGreek]

A friend of mine got fined for doing 71mph in a 70mph zone under similar circumstances. He opted for an expensive one day road safety course instead of a direct fine and licence points.

On our UK motorways we are seeing the latest HADECS3 cameras. These cameras are super accurate. They are the ones that are on a gantry shelf on the side of the motorway and not the traditional overhead type. They are also variable so if the speed limit changes due to traffic ahead, so does the camera.

At the time, the normal car speedo calibration was about a 6% to 10% overread, by law, so when he was caught the letter said his speedo must have been reading over 75mph so no defence.

However, this 6% to 10% overread is now reduced in new EU cars from 2021, again, by law, as they now have safety systems that can read roadside speed signs and automatically react. My new car has such a system, if I choose to activate it, which I don't. I also noticed the far more accurate speedo.

My 2007 Honda Civic speedo was well out, at GPS 70 it was reading 77
My 2009 Civic was slightly better and read 75
My 2013 Civic read 74
My new Honda Jazz, at GPS 70 reads 71mph.

My GPS figure agrees on my Garmin DS61, my Viofo dashcam and phone speedcam app.

That's pretty scary and very unfair. Personally, I would of gone to court and notify the police that the media would be attending. My speedo on my juke is 77 on a 70. I always follow the speedo and if I notice those shelved cameras I always to reduce to 60.
I'm in my 42nd year of driving. Never had a parking ticket. Had one speeding ticket 35 years ago.

 

[DAP]

There is no calibration that needs to be or can be done for a GPS. The accuracy is based on the atomic clocks in satellites. The instantaneous positional accuracy can be affected by atmospheric conditions, but that is a short term error that will average out in the long term. The frame rate for a dash cam may vary a few percent, but if it is paired with a GPS, the actual frame rate can be measured to extreme accuracy. So long term average speed on a GPS is extremely accurate, and counting frames against ground land marks with a GPS corrected dashcam is also extremely accurate. I would suggest that a GPS enhanced dashcam (meaning that the GPS position and timestamp is encoded in the video) is at least as accurate as any external speed measuring device.

 

[PeteTheGreek]

Admissable in Court then?

 

[Lothar]

Anyone ever been in a speeding scenario? Pulled over by a cop who said you were over the speed limit, but your Dashcam said otherwise?
What's the accuracy of a Dashcam Vs that of a Gatso or other speed trap?
Where would you stand in court?

In the US (specifically here in Maryland), cameras don't take a picture unless you're going more than 10MPH more than the speed limit. I don't think cops will pull you over for that either based on my experience.
Across the border in Virginia, I hear that they're not as lenient though. It's all about your jurisdiction.

If you are going faster than the speed of traffic, they might make an example of you.
If all cars are going 35MPH on the same 30MPH road? No cop is going to pull anyone over for speeding and bat an eyelid. If you decide to be different and go 42MPH when everyone else is going 35MPH on a 30MPH road, then yes...you will be pulled over.

 

[DAP]

If all cars are going 35MPH on the same 30MPH road?

If all cars are going 35MPH on a 30MPH road, the speed limit is set incorrectly. In the US, most speed limits are supposed to be set so that 15% of drivers will exceed the speed limit.

 

[Lothar]

If all cars are going 35MPH on a 30MPH road, the speed limit is set incorrectly. In the US, most speed limits are supposed to be set so that 15% of drivers will exceed the speed limit.

I don't think it's an issue of it being set incorrectly.
I think it's an issue of "selective" enforcement as I mentioned. If you change the road to 35MPH, then people will start driving at 40MPH because cops won't pull anyone over for doing that if all cars are going at the same speed.
Most police departments in most precincts are chronically understaffed, which leads to this kind of issue...Or maybe the police here are following the same rules as the traffic cameras which can only legally take a picture if you're going 10MPH or more over the limit?
The police are also very predictable in their enforcement in that they are usually on certain roads and certain areas of those specific roads.

There will be people who go at the speed limit of course and even under it, but those people are likely to be 60+ year olds, the elderly, and my mother.

 

[PeteTheGreek]

I don't think it's an issue of it being set incorrectly.
I think it's an issue of "selective" enforcement as I mentioned. If you change the road to 35MPH, then people will start driving at 40MPH because cops won't pull anyone over for doing that if all cars are going at the same speed.
Most police departments in most precincts are chronically understaffed, which leads to this kind of issue...Or maybe the police here are following the same rules as the traffic cameras which can only legally take a picture if you're going 10MPH or more over the limit?
The police are also very predictable in their enforcement in that they are usually on certain roads and certain areas of those specific roads.

There will be people who go at the speed limit of course and even under it, but those people are likely to be 60+ year olds, the elderly, and my mother.

And me

 

[Lothar]

If they really want to enforce this they should not create an enforcement double standard (cameras taking your picture only if you're going more than 10MPH above the limit vs an officer pulling you over for going 5MPH)...
Technically I guess that it is possible that you may get a warning for going 5MPH over the limit(I've never seen that happen either in practice), but it certainly shouldn't lead to a ticket that you have to go to court for or getting fined.

Here is Maryland State law regarding speed cameras: https://www.safezones.maryland.gov/faqs.html
There are lots of FAQs there.

Q8: If I drive past a speed camera at 2 or 3 mph over the speed limit, will I automatically get a ticket?​

A: No. In accordance with Maryland law, images are only captured and used for the purpose of issuing a citation if a vehicle is exceeding the posted work zone speed limit by 12 mph or greater.

It's actually if you're driving 12MPH above the limit that they will fine you, I just have my brain set to 10MPH to be safe and give me a buffer.

 

[PeteTheGreek]

Why not put GPS in every new car and install speed limiters.
That way it would eliminate speeding.
Oh, I forgot, they need money for the Christmas party

 

[Lothar]

Why not put GPS in every new car and install speed limiters.
That way it would eliminate speeding.
Oh, I forgot, they need money for the Christmas party

That won't have much effect because the average car on the road is around 12-15 years old.
What you're proposing would only affect new cars, and not old cars. And then every state or jurisdiction in the country also has different speed limit laws.

 

[Kremmen]

Fitting speed limiters has been deemed to be dangerous.

Scenario, you are on an, unknown to you, 50mph road and approaching a vehicle in front doing, say, 40mph. You pull out to overtake and a short distance ahead the limit changes to 40mph.

You are now alongside the other vehicle with nowhere to go other than brake hard and maybe another vehicle approaching fast.

 

[DAP]

I don't think it's an issue of it being set incorrectly.
I think it's an issue of "selective" enforcement as I mentioned. If you change the road to 35MPH, then people will start driving at 40MPH because cops won't pull anyone over for doing that if all cars are going at the same speed.
Most police departments in most precincts are chronically understaffed, which leads to this kind of issue...Or maybe the police here are following the same rules as the traffic cameras which can only legally take a picture if you're going 10MPH or more over the limit?
The police are also very predictable in their enforcement in that they are usually on certain roads and certain areas of those specific roads.

There will be people who go at the speed limit of course and even under it, but those people are likely to be 60+ year olds, the elderly, and my mother.

I believe that there are studies that show that people, on average, will drive the speed that they feel safe. There are people who strictly follow the speed limit, and there are people who see the speed limit and add 15 to whatever the speed limit is, and there are people who drive so fast they can't stay on the road, but the majority will drive what they feel is safe. It is only with excessive enforcement that people pay attention to that random number posted on the side of the road.

 

[thomas-dash]

I don't think a dash cam is going to hold up in court over a speed gun. Your best bet is to hire a traffic lawyer off of Avvo in your area and have them argue the ticket for you. Even if you were speeding, there's still things that might get you off the hook legally.

 

[Kremmen]

For many years now, at least 10, I've driven past many fixed speed cameras and in average speed zones, using my GPS speed and not the cars speedo.

So far, I've never had a single problem.

It does show, in average speed zones, how inaccurate car speeds are because I'm frequently stuck in the middle lane slowly overtaking the vehicles who I assume are using their over reading speedos.