SPECS is a computer-camera based system. As you go past the sign a digital camera reads your number plate. When you go past the next sign your number plate is read again. The computer 'knows' how far apart the signs are so it can work out your average speed between the two or three or four. The system is fully automatic and will issue a ticket without any form of human intervention. It does this for every single vehicle that passes.
You will not know you've been caught as the cameras don't flash. They work 24/7, 365 days a year, and theoretically, there's absolutely no limit on the number of tickets that the system can issue. The whole section of the M4 between Theale (J12) and Membury Services (between J14 and J15) is wired, both ways. The system is set to triger a ticket at 78 mph. Radar detectors will be of no use as SPECS is entirely passive, there is no radar or laser beam to detect.
" Fortunately, the BBC have a different view.