Going to work last night, as I passed through a Gatso at 28mph in a 30mph zone, I was overtaken by a car doing more than 30mph, I don't know if the Gatso went off but it got me thinking, how does the Gatso know which car was the one that was speeding? do they have seperate cameras inside one for each lane, as there would have been the possibility that he was keeping to the speed limit and I was speeding on the inside.