Variable message sign
A gantry structure spanning the road with electronic signals over each lane and a large MS4 message sign on the left.
The lane signals all show National Speed Limit symbols.
Between junctions 16 and 17 is the Filton Bypass, the second length of M5 to open in 1963. It was just an isolated dual carriageway west of Bristol until the M4 arrived a few years later, and only became part of a longer motorway when the M5 from Birmingham was extended down to meet it in 1971.