Non-compliant dangerous Traffic management

Network rail are currently undertaking night time working on the railway bridge on the A363 immediately off the roundabout with the A4. I have passed this road closure on 3 occasions in the last couple of weeks.The only advance warning on the east bound A4, of the A363 closure, is located approximately 50-100m before the roundabout by which time vehicles intending to turn right on to the A363 have already selected their lane. The late notice results in unsafe late lane changes both on the approach to the roundabout and on the roundabout itself as the straight ahead exit is only a single lane compared to the 2 lane approach to the roundabout. I believe Chapter 8 of ht Traffic Signs manual requires advanced warning at least 800m before roadworks affecting a high speed dual carriageway and therefore ask that someone contacts the contractors responsible and undertakes a review of the traffic management they have provided on the strategic road network.