The Scottish Executive was today criticised for pushing through proposals for a road around Dalkeith, even though the reopening of the railway is estimated to take up to 750,000 cars off surrounding roads each year.

The Borders link, also known as the Waverley Line, has received approval in principle from MSPs and is set to be up and running by 2008.

The single-carriageway A68 Northern Bypass has also been given the go-ahead by the Executive after a decade of delays.

But the proposed route through Dalkeith Park - part of Edinburgh's green belt - has sparked anger.

Campaigners from the Save Dalkeith Park group believe a "multi-modal" transport study should be carried out first, to see if schemes such as the Waverley Line do away with the need for a new road. The Executive today insisted that all other transport systems have been considered.

Jade Allison, a spokeswoman for the campaigners, said: "Transport policy has changed significantly since the road was originally authorised.

"There is now an emphasis on trying to reduce reliance on the car.

"With a strong likelihood of the Borders Railway being rebuilt, how can the traffic assessments for the road still be accurate?"

The three-mile bypass is set to run the north-east of Dalkeith, linking the A720 to the A68, and was given planning permission in 1993 after a public inquiry.

The campaigners battling to save Dalkeith Park have won the backing of the Green Party and transport lobby group TRANSform Scotland.

Director Colin Howden said: "The traffic modelling [for the bypass] dates from the early 1990s, while the framework dates from the late 1980s. This boils down to the absence of a multi-modal study, which means the whole basis for the project is out of date."

Mark Ballard, Green Lothians MSP, added: "It's crucial that the full impact of changes in the transport network - in particular the A7 bypass and the proposed Waverley Line - is taken into account as part of a complete re-assessment of the A68 Dalkeith bypass.

"The new rail link has the potential to take hundreds if not thousands of cars off the roads. The minister should urgently reconsider the plans to ensure that both value for public money and the environment are prioritised."

An Executive spokeswoman said: "Traffic studies are being carried out and full assessments were also carried out at the time [of the decision].

"These were over and above the requirements. The bypass will compliment other transport systems, including public transport."