Pam mae gan yr M48 rhwng Gwndy a Chas-gwent derfyn cyflymder o 50mya, sydd wedi bod yn derfyn dros dro ers bron i dair blynedd oherwydd rhwystr nad yw'n cyrraedd safon ddigonol, tra bod gan ffordd unffrwd arferol heb unrhyw rwystr o gwbl derfyn cyflymder o 60mya?
The 50mph speed limit on the M48 between Undy and Chepstow has been introduced as a safety measure due to the condition of the central reservation barrier.
Motorways are designed to operate safely at higher speeds because they include safety features, such as central barriers, which are intended to contain and redirect vehicles in the event of a collision. On this section of the M48, the existing barrier has reached the end of its serviceable life and no longer provides the level of protection required for operation at the national speed limit.
In these circumstances, it is appropriate to reduce vehicle speeds to manage risk. The current speed limit has been set following an independent operational risk assessment. Lower vehicle speeds significantly reduce both the likelihood and severity of collisions, including the risk of vehicles crossing into opposing traffic, which is a key safety consideration on high-speed dual carriageways such as motorways.
While this may appear inconsistent when compared to single carriageway roads that have a 60mph national speed limit without a central barrier, the two situations are not directly comparable, and design standards are different. Speed limits are determined by the overall design and risk profile of each road. Motorways rely on a functioning central barrier as a critical safety feature to safely accommodate higher speeds and traffic volumes. Where that feature is compromised, it is necessary to reduce the speed limit accordingly.
The Welsh Government has developed and funded a scheme to replace the road restraint system on this section of the M48 and is working with partners to commence these works. Once the new barrier has been installed and the route meets the required safety standards, the intention is to restore the national speed limit. (Saesneg yn unig)