Finlay Carson, MSP for Galloway and West Dumfries, challenged the Scottish Government over its commitment to improve the road, which is the main route from Belfast to mainland Britain and Europe and carries an estimated £17 billion of freight each year.
He spoke out after it was revealed some goods are now being shipped between Northern Ireland and English seaports instead of via Cairnryan, due to the poor condition of the A75 and its unreliability record.
One logistics company confirmed it had now reduced the amount of freight being shipped via the A75.
AM Logistics in Northern Ireland said: “We were running out of time using the A75. We move goods from Northern Ireland via Scotland to, for example, the English Midlands, and we want to do it and be back up through Cairnryan in a ten-hour window.”
The firm warned: “It could come to none of our freight going via Scotland. Cairnryan is a major port and the roads which service it just aren’t good enough.”
Speaking in Holyrood last Thursday, Mr Carson said: “First Minister, a recent review by Sir Peter Hendy for the UK Government has found the A75 is the road most in need of an upgrade anywhere in the country.
“Will you admit that the failure to upgrade this dangerous road, often referred to as a goats’ track, represents a broken promise to the people of the South West of Scotland and the haulage and ferry companies that depend on the route to move goods to and from Northern Ireland?”
Responding, Nicola Sturgeon refused to accept his opinion and said: “The STPR2, of course, recommends that safety resilience and reliability improvements are made on the A75 corridor to support access to Stranraer, and to the ports at Cairnryan.
“We will continue to take decisions that do, indeed, support that access that all of us accept and agree is extremely important.”
Afterwards Mr Carson said: “How many times down the years have we heard promises from the SNP Government that it will improve the A75 – it is almost like a broken record.
“Surely the fact that firms are now bypassing Scotland because of the state of the A75 and choosing instead to sail from English ports says it all that this should now be a top priority for this government?”
