How frustrating at 11.30pm with nothing on the road. I can understand perfectly at rush hour (Friday evening was much better than normal and I guess it was down to the slightly slower traffic not messing up the lane changes just before the newport/carleon bit where the inside lane is reserved for people going off the M4)... wish it was a 7am - 10pm and 4pm - 7pm thing only (or something like that), though...

The M1 at Luton was like this for ages.. it's a total nightmare. Travelling up there at 11pm was such a nightmare I generally used to take the M40 just to make some more progress.

This looks like a permanent speed limit - they've put up proper signs anyway.