The A75 is not only the road to Stranraer and the ferry ports of Cairnryan but, as such, is also the road to Belfast, one of the UK's capital cities.
Due to the current design of the road and previous fact, it is a road where many differing vehicle types are thrown together often at highly differential speeds. The volume of HGVs in convoy travelling east when the ferries dock combined with the 40mph limit for those vehicles causes very high level of congestion upon the A75, a volume of traffic that was never envisioned when the current road was designed.
Throw in even slower moving agricultural vehicles, faster moving traffic, such as cars and motorcycles, and a large amount of tourist traffic unfamiliar with the vagaries of the A75, and it is easy to see how frustration can brew carelessness on the road. A change to dual carriageway would help negate the causes of this while also preventing a conflict between vehicles travelling east with those travelling west.
For the same reasons, the local economy would benefit by being more accessible to tourists, commerce and improved links with Northern Ireland and England. This is not to mention the benefits to the local populace in improved safety and reduced journey times, especially when there is more centralisation of health services to Dumfries resulting in journeys of up to 90 miles for some in the west of Dumfries & Galloway.
I have come to these conclusions as a regular user of the A75 and I know for a fact that I am not alone in holding these opinions.