Re: Execu-barge
They're put in because they're required to enforce 20 mph areas. The possibility that they might cause damage leading to an accident outside the area isn't a concern because obviously the cause can't be traced back. The road safety industry is very good at denying its the consequences of its actions. It's currently working hard at denying that "smart" motorways* are dangerous.
At the same time they ignore dangerous features: I know of one stretch of road which has notices up along the lines of X casualties in 5 years (not very specific as to which 5 years as the notice has been there for at least 10). That stretch of road has 4 junctions with extremely poor sight lines including an oblique cross-roads with another A road which very clearly needs a roundabout. The only remedial action has been to reconfigure the major crossroads to make it even more dangerous and to provide onesmall, inconspicuous convex mirror.
*Probably somebody thought it smart to add an extra lane without having all the hassle and cost of widening the wayleave.