It’s all just a complete waste of time – example of the Welsh Government taking a macro problem – such as emissions and then applying a solution of very little effect to the problem with a complete disregard for the local (micro) area problems that it will cause end road users.
If the actual end benefit is saving lives through lowering pollution then it’s stupid as the % chance of a life threatening accident occurring is increased due to the aforementioned speed issues on slip roads.
If the end benefit is to improve environmental goals for Wales then stop mucking about with this and get cash to do the Swansea Tidal lagoon instead.