Hell, let's just police everyone's hard drives just in case, you know? Isn't catching pedophiles a good thing, after all?
Cellphones have been doing this to all of us for decades.
But when you’re driving a deadly vehicle on public roads, you don’t have a legal right to privacy that’s the same as if you were on private property.
Laws first, then we’ll talk about cameras.
That said it does need to be more complex because to produce as few false positives as it can, which would cost BusPatrol money to review in their first pass before sending to police (so there's at least a minor incentive to reduce them), they would have to determine where the car is and if it's required to stop not just trigger if a car passes by while the arm is out. Laws vary a lot by state but usually if there's any kind of real median traffic in the opposite direction is not required to stop so it would at least need to detect if that is present (or work off a database that knows where all the divided roads are in the area I'm not sure which would be cheaper but mapping feels harder and having the camera able to determine if there's a median can be deployed anywhere while mapping data is location specific).
I think the 80s machines used something more like hand built digital image processing to find the characters, but OCR is absolutely not new.
You can say that we should only restrict this to critical safety situations, but it becomes a very slippery slope once cities start to see that revenue coming in. In some situations, cities have contracted private companies who profit on every ticket their cameras issue - that creates a huge conflict of interest and incentive for them to keep tuning the cameras to catch more and more 'offenses'.
An automated fine is the least painful way to enforce that.