Dumfriesshire Clydesdale and Tweeddale MP David Mundell has expressed disappointment that a Conservative motion to improve Leadburn junction has been rejected by members from other parties on Midlothian council.
The busy road crossing north of Peebles is used by traffic on the A701, A703 and A6094 routes.
Mr Mundell said: "Constituents have contacted me over many years with concerns about Leadburn junction and the consensus has been that a roundabout is the best solution.
"I've heard repeated accounts of near-misses and it seems wrong, particularly at such a busy and strategically important junction, that we appear to need to wait for a major tragedy in order to justify such essential investment."
Mr Mundell was encouraged by an ongoing offer by Scottish Borders Council to work closely with Midlothian Council on a Leadburn solution.
The MP last night renewed his offer to support local authority and Scottish Parliament colleagues who planned to continue campaigning for improvements.
Earlier, Shona Haslam, Conservative leader of Scottish Borders Council, was equally unhappy that the Midlothian Council motion seeking to improve the Leadburn 'backspot' had been turned down by a majority of councillors.
She said: "Scottish Borders Council will continue to push for improvements and stand ready and willing to work with Midlothian to find a solution."