A TEES Valley metro system could destroy a historic rail line, according to a union.

Aslef, the train drivers' union, has said the proposed £150m train system that would link Saltburn with Darlington could spell the end of the Bishop Auckland to Darlington rail route.

This route, run by Northern Rail, is part of the Bishop Auckland to Saltburn line, and is infrequent and under used, according to John Clark, Darlington Aslef secretary.

The metro would link Darlington to Saltburn using a mix of new and existing facilities, including five new stops serving regeneration and employment sites, including Durham Tees Valley Airport.

But Mr Clark fears that if the Tees Valley metro replaces the Darlington to Saltburn section of the route, the Bishop Auckland to Darlington line would become unsustainable, leaving the Wear Valley without a train service.

The metro proposal has been put together by Tees Valley Regeneration with support from the five Tees Valley councils.

Mr Clark says that there has been a lack of consultation, and he and Aslef believes that existing rail services could be upgraded and improved at a third of the £150m proposed.

He said: "The authorities on Teesside are determined to push through this scheme and suppress consideration of alternatives.

"This figure of £150m does not add up, it could be done for a third of that and I don't understand why this can't include Bishop Auckland."

Joe Docherty, chief executive of Tees Valley Regeneration, said that if anything, the metro system could boost the Bishop Auckland to Darlington rail service.

He said: "We know his concerns are well intentioned and there will be an opportunity early next year when there will be wide consultation."

The idea is that new track would be laid alongside existing rails, therefore freeing up congested rail junctions, allowing more freight trains and long distance services to run through the Tees Valley.

A recent Government report may hamper the case for a Tees Valley metro system. It said: "Trams and heavy rail should only be considered as an appropriate policy intervention once an urban area reaches a sufficient density. They are not likely to be the most cost-effective where transport corridors are more sparsely populated."

The report says that unless passenger figures reach 6,000 per hour, heavy and light rail systems are unlikely to prove good value for money.

As a comparison, on its busiest days about 100,000 people use the Tyne and Wear Metro every day - an average of 5,800 an hour.

Darlington MP Alan Milburn met local MPs yesterday to update them on the progress of the proposed Tees Valley metro.

Northern Rail did not return The Northern Echo's phone call.