The methods employed to catch people speeding on the M6 remain a mystery despite thousands of motorists being issued tickets by a fleet of 'secret' cameras.
Following an in-depth investigation, Birmingham Live found that police and roads authorities could not provide information on the ways these motorway speed cameras, which monitor drivers in temporary speed limit zones, are having such success - more than 3,500 have been clocked breaking the temporary 40mph speed limit on one stretch of motorway this year alone.
It is likely that drivers are being caught en masse during specific periods when the cameras are switched on and the normal speed on the motorway has been slashed.
