WITH a price tag of £692 million - or £2,000 an inch - it is Scotland's most expensive road. But when it finally opens tomorrow, three years late and nearly three times over budget, experts fear the M74 extension in Glasgow could simply generate more traffic and do little to ease the country's most chronic congestion.
The six-lane motorway will extend the M74 for five miles through the south side of Glasgow to join the M8 west of the Kingston bridge over the Clyde.
It is designed to ease traffic jams on the M8, which has been snarled up for several miles through the city centre at peak hours for decades.
The Scottish Government's Transport Scotland agency, which is in charge of the project, said the road was due to open to traffic at 7pm tomorrow after "final operational and safety checks" following its official opening by the Duke of Gloucester at noon.
But transport experts have told The Scotsman the new road will encourage more traffic and the M8 could clog up again as the economy recovers. And while motoring and business groups said the project would bring major benefits, environmental campaigners, who mounted a legal challenge to the road being approved, said the scheme was folly.
Colin Howden, director of sustainable transport group Transform Scotland, said: "I think it would be reasonable to expect an initial reduction in traffic congestion across Glasgow, but that this will be eroded as extra trips are generated. So I wouldn't be surprised to see the same levels of congestion on the Glasgow road network within a few years."
The extension was approved by ministers despite being rejected by an independent public inquiry.
The Scottish Government has trumpeted the 445m construction contract - which excluded the cost of decontamination and land purchasing - as being completed early and under budget, but the overall cost of the project has rocketed and the road's completion is in fact years late.
It should have been finished three years ago, and when initially given the green light in 2001 was estimated to cost 245m.
Glasgow Green MSP Patrick Harvie, the past convener of Holyrood's transport committee, said: "The evidence is clear - building new motorway capacity, like the M74 extension, just creates more congestion, not more jobs.
"In the longer term, Glasgow can expect slower journeys, worsening air quality and more cost to the local economy."
Stephen Joseph, chief executive of the Campaign for Better Transport, said: "The promoters of the M74 have never been prepared to take seriously the idea that the road will suffer from the 'M25 effect', where it generates so much traffic that jams get worse rather than better.
"This effect is now well recognised worldwide, but the danger is that instead of learning from it, the Scottish roads authorities will simply come back for more and try to build even more roads across Glasgow."
The public inquiry report into the project in 2005 concluded the road "would be very likely to have very serious undesirable results" such as encouraging more traffic.
The report forecast significant traffic queues at the south end of the new road, at Fullarton, and Transport Scotland said it would monitor M74 and M8 traffic merging at the north end, at Dumbreck, for any problems.
Further evidence of the likely short-lived improvement provided by the M74 extension came from research commissioned as part of Glasgow airport's latest development blueprint this year.
It stated: "The M74 is expected to ameliorate peak period congestion on the M8 in the short term. This is, however, expected to be nullified in the medium to long term as traffic volumes grow."
Ben Heydecker, professor of transport studies at University College London, said: "I would expect an increase in traffic with any road expansion." He said it was likely other vehicles would take the place of those currently using the M8 switching to the M74, and added "how much, we will find out".
Derek Halden, of Edinburgh-based transport consultants DHC, said: "Car ownership in Glasgow is very low. There is a very large potential for traffic growth, and household surveys show people in the east end are particularly keen to get cars and drive more.
"The impacts (of the M74 extension] on the M8 are less easy to predict but it is likely that many more local, short trips will be made.
"If new jobs are also attracted to the area, then this will also help fill up the motorway. The weak economy has, however, limited the growth in traffic, so the new motorway may not fill up with traffic as fast as people might worry about."
And Dr Iain Docherty, professor of public policy and governance at Glasgow University, said: "Research suggests a modest traffic reduction on the M8, but we will have to see how traffic will react."However, the case to build the road was based on its economic generation potential, which I am quietly optimistic about."
The M74 building contract attracted just one bid, from a consortium of major construction firms who teamed up as Interlink M74 JV, a joint venture comprising Morrison Construction, Balfour Beatty, Morgan Sindall and Sir Robert McAlpine.
The Scotsman understands the cost of the three-year contract was higher than hoped, but Transport Scotland was prepared to accept it in return for all the risks involved being transferred to the contractors.
The project, a partnership of Transport Scotland, the principal funder, and Glasgow, South Lanarkshire and Renfrewshire councils, has also been severely criticised by the public spending watchdog. Audit Scotland attacked the project's poor management and planning.
Motoring organisations remained convinced of the traffic benefits, but some acknowledged levels would increase.
Philip Gomm, a spokesman for the Royal Automobile Club Foundation, said: "We are all driving less than we used to, but overall there is likely to be increased road traffic as the Scottish population grows and the economy recovers."
Neil Greig, the Scotland-based policy and research director of the Institute of Advanced Motorists, said: "It will not be a complete panacea, as the two lanes through Charing Cross will still struggle at peak times, but delays should be reduced and journey times become more predictable."
Paul Watters, head of roads policy for the Automobile Association, said: "It is inevitable that other localised traffic pressure points may develop in the longer term, but that may be a price worth paying for the benefits this extension brings in terms of access, safety and to the economy."
Business leaders also insisted congestion would be eased.
Scottish Chambers of Commerce head of policy Garry Clark said: "Almost every vehicle using the new road will be a vehicle less on the Charing Cross to Baillieston stretch of the M8."
CBI Scotland policy executive Lauren McNicol said: "This project has been a long-standing priority for our members and will play an important role in alleviating the pressure on the busiest stretch of the M8 motorway through Glasgow and improving connectivity, which is essential for the success of Scotland's economy."
A Transport Scotland spokesman said: "When it opens on 28 June, the M74 Completion scheme will provide improved access to economic, employment and education opportunities for the people of Scotland.It will improve journey times and reduce traffic congestion on roads across Glasgow and South Lanarkshire - removing approximately 20,000 vehicles from the M8 between Baillieston and Charing Cross, as well as reducing up to 15 per cent of traffic from local roads, such as at Rutherglen Main Street.
"In addition the M74 Completion is expected to reduce road accidents by 25 to 35 each year on average in the 20 years after opening, as well as improve air and noise quality on local roads."