The signage is a disaster on these roads. Lane closures are a very unobtrusive red X and not posted frequently enough. Text is too short and doesn't indicate how far ahead any hazard might be. Some signs are in a different style (small board overhead rather than a gantry across all lanes) which can easily be mistaken for an advisory notice not a command/prohibition.

Worst of all, the signs are almost always massively out of date and present a false alarm. You'll see a lane closure and very short text "obstruction in road" sign but then nothing actually there. I don't do huge mileage on these roads and I've probably come across this false alarm scenario 40 or 50 times, and never seen an actual hazard which was signed.

It's not at all surprising they get ignored by a significant minority of drivers.

That's why they need actuated spikes...

It's pretty hard to keep driving at dangerous speeds when your tyres are flat...

Ignore the signage and you'll be buying new tyres... That will soon have everyone paying attention to the signs.