I know this road well, there are two major problems.
Firstly the road most of the day is saturated with traffic, in both directions making overtaking very dangerous and pointless, as a major route there are large numbers of heavy lorries, and farm traffic.
There are some stretches where, under the right conditions, overtaking might be possible but the are marked up to stop overtaking, which adds to the frustration.
The other difficulty is, side roads or cross roads, people get frustrated waiting to join the A road or cross it, so they chance it.
In some there are central reservations but these tend to add to the confusion as the reservations have no lane markings.
The position of the vehicle in the reservation doe's not give much indication of the drivers intentions.
At some junctions with a reservation, the A road changes to two lane but if anyone on the A road tries to cooperate with the B road drivers others on the A road try to use the very short stretch of two lane to overtake.
Traffic lights would be one solution, I was told by one local traffic engineer that the density of traffic on the A road is too high for roundabouts, and they would too expensive?
Anyway, I don't see how dropping the 60MPH to 50MPH is going to serve any useful purpose.