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You can detect speed,ount and types ofcas with a pair of inductive loops (car length determines the type pretty well). I'd guess that putting such a pair some distance before the intersection would be a lot simpler (cars would obscure each other in the camera's view). That said, this would give you information about cars passing a single point on the road and would give you no information about pedestrians.

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This has been implemented for some traffic lights in Warsaw, and has one more bad side effect (possibly because of bad implementation): if you a bike in the late evening on the smaller street, that's configured "red unless there's a car that will be crossing" to maximize throughput of the bigger street, you have to wait for a car or use a pedestrian crossing, because the loops won't detect a bike.

Lots (most?) of the traffic light controlled junctions in the UK have induction loops to detect cars. I have personally complained to the authorities about their lack of ability to detect bicycles.

Inductive loops, wires, maintenance, etc., are far more expensive than a $10 camera, once the software is developed.

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