e-Toll Gantries: How they work

Kelerei said:
The FE-Schrift typeface (which is used on South African license plates) is specifically designed to mitigate this problem. From Wikipedia:



The biggest issue will likely be the quality of the OCR software.
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Yeah, but now throw a splotch of mud that covers a significant area of the plate, like a whole letter and speckles over the rest of the plate... there's a reason they want e-tags.
 
Lukcydog said:
I used to work in this field so I can give a basic idea. The tag is based on RFID technology, so in theory when you drive through the gate, the RFID is triggered to pulse its information to the gantry. This is the easy solution for e-tolling.

You will see that there are the black lights and cameras posted next to each other. The white area of a car's number plate is designed/painted to reflect black light which are then picked up by the cameras as a black and white image. You will also see that there are paint markings on the road under the gantry that are used as trigger points. The trigger points initiate the taking of pictures as well as determining the class of vehicle currently passing the gantry. They then have a server/s that process the images to retrieve the number plate, length of vehicle. They also take a picture of the vehicle as part of the record in case of a dispute from clients. The problem with number plate recognition is the fact that typical accuracy is 94% (to reach 98% accuracy starts costing so much its not feasible), which leaves a massive margin of undetectable plates. So if a plate can't be recognised automatically, they have to manually annotate the "toll" which will be at cost to them. I don't know what camera's they are using but we used to use ARHungary's product (currently running at ACSA aiports when you go into the parking area where you pull your ticket) which is incredibly fast, very accurate, but very very expensive. The one used for e-toll look like a cheaper solution. So SANRAL want you to use tags, because it makes they life very very easy in terms of maintenance and effort.

I hope someone finds this interesting.
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Yup... this whole post exactly. One of the cameras will likely have an infrared (or UV) filter that will only pick up infrared or UV light. This way only the reflective part of the number plate is visible to the camera, making OCR easier. If it's infrared, it's easy to screw up the cameras with a few infrared LED's. I wonder if they are using the same concept but with UV though? They will have full colour images as well, so you need to obscure the plate in some way if you want to prevent manual detection by an operator... and not have an e-tag.

As for the tags... if they are RFID tech... they would have to be IPX tags as EPC tags are useless above 80km/h... and even IPX tags don't pick up over 160km/h (but if you are doing that through a gantry I guess you'd get a ticket if your plate didn't have mud:P) Also, the transmitters would have to be f'ing powerful to get any kind of decent range. I'd imagine that they'd have some kind of active tag technology to get the range they'd need.
 
Messugga said:
I can't speak about accuracy, but having discussed their capabilities with one of the senior techs, these cameras seem to be very, very fast.
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Oh yeah, there's no way in hell you'll blur a camera using speed if that's what you mean. Their shutter speeds are ridonculous.
 
Messugga said:
Not only that, but frame rate as well.
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Yeah, the frame rates can easily get over 100fps... but even at 60fps it's the shutter speed that counts. At 100fps you can pick up someone several times (more than 5) in the space of a gantry's distance at over 250km/h. Heck even a gopro can do over 100fps these days.
 
I am interested in the inner and outer workings and have started to think of a few scenarios:

  • What if you have a dot on your car bonnet that delays the trigger for the camera. Would that cause some problems with the plate recognition?
  • If you drive at the back of a big truck the chances of the camera identifying your front and also the size would be a problem right?
  • Would there be a blind spot (very fine one), so if you change lanes just at the correct time your number plate will get split between two cameras?

I know quite weird questions but just thought about these things quite a lot lately.
Would love to know what others think.
 
cnever said:
I am interested in the inner and outer workings and have started to think of a few scenarios:

  • What if you have a dot on your car bonnet that delays the trigger for the camera. Would that cause some problems with the plate recognition?
  • If you drive at the back of a big truck the chances of the camera identifying your front and also the size would be a problem right?
  • Would there be a blind spot (very fine one), so if you change lanes just at the correct time your number plate will get split between two cameras?

I know quite weird questions but just thought about these things quite a lot lately.
Would love to know what others think.
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The cameras are video cameras. They don't take single pictures, so there's nothing to trigger.

The angle of attack that the cameras need to be able to identify your plate is very aggressive. They can read your plate with something like a 30cm gap between cars. Also, they get both the front and rear plates, so you would need two trucks driving terribly close.

Doubt that there will be a blind spot when splitting lanes. I know the cameras' field of view overlap very, very slightly. If you're good enough to get them to only get a partial plate that way, you deserve not to pay the toll.
 
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Messugga said:
The angle of attack that the cameras need to be able to identify your plate is very aggressive. They can read your plate with something like a 30cm gap between cars. Also, they get both the front and rear plates, so you would need two trucks driving terribly close.
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I would imagine that, that figure is if you're following another passenger vehicle otherwise you're saying that the cameras can do OCR at nearly vertical angles.

Assuming that your front number plate is 0.5 meters above the ground and the car in front of you has a boot 1.5 meters high (normal sedans) then the maximum down angle is 73 degrees (17 degrees from vertical).

Using the 17 degree figure, if you were driving behind a 4.3 meter tall truck (standard regulations), you'd have to drive no more than 1.14 meters behind the truck to obscure your front number plate.
Now angle your front number plate downwards by 15 degrees and your following distance only needs to be 2.37 meters or less.
Put some mud on the back plate and tail a big truck and you're sorted.
 
Paul_S said:
I would imagine that, that figure is if you're following another passenger vehicle otherwise you're saying that the cameras can do OCR at nearly vertical angles.

Assuming that your front number plate is 0.5 meters above the ground and the car in front of you has a boot 1.5 meters high (normal sedans) then the maximum down angle is 73 degrees (17 degrees from vertical).

Using the 17 degree figure, if you were driving behind a 4.3 meter tall truck (standard regulations), you'd have to drive no more than 1.14 meters behind the truck to obscure your front number plate.
Now angle your front number plate downwards by 15 degrees and your following distance only needs to be 2.37 meters or less.
Put some mud on the back plate and tail a big truck and you're sorted.
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Covering anything on your number plate on purpose is illegal, so there's that...

Anyway, with regards to your angles: you are correct, but it requires you to drive between ~4.3m tall tracks with a distance of no more than (let's add some fat) 3m between you and said vehicles, at 80km/h (because trucks don't do 120) on the N1. To me that sounds like a recipe to get yourself killed rather than avoid paying any tolls.
 
Messugga said:
Covering anything on your number plate on purpose is illegal, so there's that...
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Of course but if your vehicle is plastered with mud or your rear number plate "fell off" ...
Easy enough to argue with officers and you're unlikely to be pulled over every day.
People without any plates on their vehicles are seldom pulled over in full view of metro police.
 
Paul_S said:
Of course but if your vehicle is plastered with mud or your rear number plate "fell off" ...
Easy enough to argue with officers and you're unlikely to be pulled over every day.
People without any plates on their vehicles are seldom pulled over in full view of metro police.
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I somehow suspect that is going to change now that e-tolls are live. ;)
 
genetic said:
I somehow suspect that is going to change now that e-tolls are live. ;)
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It has already... am hearing stories of people being nailed this week for idiotic crap to do with number plates.
 
Koosi said:
It has already... am hearing stories of people being nailed this week for idiotic crap to do with number plates.
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Probably about the only positive outcome regarding e-tolling.
It just proves that law enforcement is about money and not safety.
 
Yesterday i had to go past three toll gantries for work. I went through them in the middle (ie not covering marks in the road). I see this morning, that those three tolls have been recorded.

Anyone seen if it works in the rain? I know the system in Cape Town is very sensitive to rain (ie refraction of the "light" through the droplets)
 
Lukcydog said:
Yesterday i had to go past three toll gantries for work. I went through them in the middle (ie not covering marks in the road). I see this morning, that those three tolls have been recorded.

Anyone seen if it works in the rain? I know the system in Cape Town is very sensitive to rain (ie refraction of the "light" through the droplets)
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The e-tolls don't use simple technology. They are quite sophisticated. They don't take pictures, they take continuous hi-res video and use sophisticated software to decipher car type / OCR from numberplates etc. I'm sure they designed the gantries with rain in mind. ;)
 
genetic said:
The e-tolls don't use simple technology. They are quite sophisticated. They don't take pictures, they take continuous hi-res video and use sophisticated software to decipher car type / OCR from numberplates etc. I'm sure they designed the gantries with rain in mind. ;)
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I should check how our cameras here work in the rain (considering they cost R10k apiece, excl IR emitters) with the licenceplate recognition system.
The problem is however, when the rain stuffs with the visibility.
 
So I've only gone through about 5 gantries (2 way trips), So 10 in total and it says I have gone through 15 gantries. Anybody know who I can contact to get proof that it was indeed my vehicle?
 
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