I’ve seen the number of induction coils increase drastically over the years in The Netherlands. They are quite easily recognizable, as there’s typically a solar panel on a pole, that appears to provide power to the system.
Considering there’s a wide variety of vehicles on the road, surely each variant must have (slightly) different characteristics when passing over the coil; especially when in a specific place at a specific time.
And given that they are situated at highway exits (see picture) or after entrances, and road users unable to exit and enter elsewhere, it would be trivial to track the bulk of a vehicle’s trip.
This in context of ALPRs (in different forms) being in place at strategical locations (large junctions or at bridges or tunnels, and parking), and the address of vehicle’s owner; you’d be able to connect the dots, and end up with a pretty complete picture.
I wonder how financially constrained a nation state is, where such projects typically follow a public tender process; the scale of the project could by itself, or maybe in coordination with other nation states, benefit from economy of scale; and where prices for components have increased sharply over the years. Other than that, perhaps you could have dedicated sampling hardware, which is able to convert the stream, to one manageable to an off-the-shelf PLC; which might not do any complicated processing on-edge, but instead transfer the data to a data center for further processing. But I have no expertise in the field, so I could be completely and utterly wrong.
As a person who has some expertise in a related field, let me explain:
If the covered area represent coils, those coils are not appropriately sized or positioned to detect differences from car to car. They are appropriately sized to do what the other poster said and provide a presence input that can be used to feedback into a traffic control system or a simple counter to analyze road use.
A current is induced in a coil when a ferrous material is vibrated near it or when an electric current flows near it. The frequency, intensity and wave shape of the current is directly proportional to the movement of the ferrous material or flowing current. The degree to which the current is induced is modified by coupling strength and the structure of the coil.
A coil that size would be really bad for receiving induced currents that reflect various relatively small ferrous moving parts like pistons and wheels whose particular signatures could be used to identify a vehicle and also bad for receiving induced currents that reflect electrical activity which could also be used to identify a vehicle.
It is the right size for receiving induced currents that indicate a large ferrous object like a car has passed near it.
Which is of course what a coil like that is used for in civil engineering.
Each detector seems to have two coils (see picture), which appear to be an emission coil and a reception coil; similar to metal detectors with a DD coil. Typically these coils slightly overlap to increase detection sensitivity; but this doesn’t really seem necessary when a massive block of metal hovers directly over the coils. Each coil likely consists of multiple turns of wire, that sit on top of another inside a groove cut into road surface; which should increase the inductive properties.
The magnetic field also induces Eddy currents in non-ferrous metals (meaning currents running through metal within the field), which by themselves generate opposing magnetic fields, depending primarily on the material’s conductive properties (highly conductive materials yielding stronger magnetic fields). These fields change the phase of the received signal, which in metal detectors can be used as an indicator for material properties: primarily the type of metal and its mass.
If the same were possible on the traffic detectors, or even a signature of metal concentrations, I believe you’d have a pretty robust identifier for vehicles.