Looks to me as if they most likely aren't regular speed cameras, the devices appear to be some kind of traffic monitoring system as seen on many major roads around Thailand.
Advanced Traffic Monitoring System: uses multiple cameras to track traffic flow, identify vehicles (including stolen ones), and even monitor for accidents. If near an intersection they may monitor red light jumpers. Thy may capture license plates of vehicles that pass through check licence and traffic density.
Oddly enough I got a speeding ticket (and photo) near there about 11 years ago - 500 baht.