JOBS NOT so much a motorway, more a jobs machine.

The M74 Completion - or M74C for short - has always been about employment. In two decades, its backers contend, the road could bring 20,000 jobs to communities along its five-mile length, almost one for every foot of tarmac to be laid.

That figure isn't without its critics. Forecasting employment levels isn't an exact science. But, for the record, economists worked out that the M74 would boost the competitiveness of the west of Scotland economy enough to draw 11,000 extra jobs to Glasgow, 4000 to West Renfrewshire and around 3000 each to South Lanarkshire and East Renfrewshire. Even relatively distant North Lanarkshire and East Dunbartonshire would gain, respectively 1500 and 500 posts.

The forecasts, in a report from consultants Simmonds, were exactly what M74C backers wanted to hear. Local businesses clearly wanted to see growth. Politicians wanted to see growth in the areas of Scotland, like the east end of Glasgow, where they thought it was needed most.

The reporter who oversaw the public local inquiry into the M74C wasn't impressed by the Simmonds figure - and not necessarily because he disagreed with them. It was just that they did not tell the whole story. The jobs, said Richard Hickman, would be created with or without the motorway. But not in and around Glasgow.

Simmonds based their calculations on a fixed number of new jobs being created in the Scottish economy. So any new job in, say, Glasgow, meant foregoing extra employment somewhere else. With the M74C, the firm said, there would be 8000 fewer posts in the Forth Valley; Ayrshire would lose 3000; Inverclyde 1500.

Mr Hickman, whose findings were rejected by the Scottish Executive in 2005, ruled that the road would make "a positive contribution to local economy" but "at the expense of the Forth Valley, the Stirling area, Ayrshire, Inverclyde and Dunbartonshire".

"He just completely missed the point," said one backer. "The whole point was to centre economic growth in an area that was underperforming." People will follow the jobs. As many as 14,000 individuals could relocate to Glasgow and the west thanks to the M74C.

REGENERATION THE M74C isn't just a road through Glasgow. It's a road to Glasgow too.

The proposed five-mile route of the M74 extension runs from Fullarton junction near Carmyle in South Lanarkshire to the M8 just west of the Kingston Bridge in Glasgow.

It will pass over some of the most contaminated and polluted parts of Scotland, transforming an urban waste ground into lucrative business and residential neighbourhoods.

For some years Glasgow planners have seen the motorway as the main engine for the regeneration of the east end of the city. Even the suggestion that the road will come has already helped secure investment - not least the Commonwealth Games in 2014, three years after the M74 is finally completed.

The Games have been widely championed as a vehicle to regenerate the east end of Glasgow and should help lure thousands of new homes and scores of businesses.

What is more important, the M74 or the Commonwealth Games? Few Glasgow figures were prepared to say yesterday. "It would be like choosing between my children," said one decision-maker.

The Commonwealth Games - whose benefits are far wider than economic - are expected to create 1000 permanent jobs; a fraction of those brought by the new motorway alone.

In fact, the cost benefit ratio for the M74C is almost off the scale, at 1:16 in 1999. That compares with 1:4 for other transport projects, like the M77, which were given priority over it.

One policy-maker called the M74C "our Olympics". The road, he said, would do for Glasgow what the 1992 Games did for Barcelona. Even the road's stub - built under the Tories in the early 1990s to bring the M74 as far into the city as Carmyle, has proved that point.

When Weir Pumps began looking for a new home earlier this year council officials in Glasgow could only find one suitable site to offer them, near the M74 in Carmyle, The Herald understands. Another new road, the East End Regeneration Route, is planned to link the M74 right into the heart of Scotland's poorest communities and lucrative industrial gap sites.

Jim Fairbairn, chief executive of Clyde Bergemann, a manufacturing firm in Bridgeton that exports to 70 nations, is already seeing the pressure on the east end's regeneration. "The amount of traffic in the east end has doubled in the last 10 years. Sometimes we are struggling to get our lorries in. We desperately need this road."

TRAFFIC IS the M74C a good idea? "Ask somebody sitting in a traffic jam at the Kingston Bridge," said Lesley Sawers, chief executive of Glasgow Chamber of Commerce. "Ask anybody who is in the distribution or sales business trying to make a delivery or anybody trying to commute to work. We have got to re-route traffic off the M8."

Something like 180,000 vehicles use the Kingston Bridge over the Clyde every day, many at a snail's pace. The universally loathed crossing was only designed to carry 20,000 when it opened four decades ago. The bridge is now - as anybody listening to morning and evening traffic bulletins - the biggest logjam in Scotland.

Ms Sawers believes it is costing business money. "The time lost has a price in commercial terms, never mind quality of life. It plays a part in why Glasgow has such low productivity."

The new M74C would take much of that pressure off Glasgow's road network, diverting cars, lorries and buses on a shorter and more direct route from east to west. The M74C is expected to cut the number of vehicles on the M8 between Baillieston and Charing Cross by 20,000 a day. Some sources reckon the new motorway would take 28,000 cars off the Kingston Bridge alone.

So what will these cuts in congestion do to journey times? Project backers claim they will shave five to 10 minutes off cross-Glasgow trips. Journeys from EuroCentral, the business and transport hub at Mossend, Lanarkshire, to Glasgow Airport will be cut by six minutes. From Hamilton to the airport, the saving is even bigger, some 12 minutes. Journeys will be quicker from south to north too. The new towns of Cumbernauld and East Kilbride will be five minutes closer.

The M8 is not the only congested road in Glasgow. Others too could be freed up. Modelling carried out on behalf of Glasgow City Council shows other local roads, especially streets like London Road currently used as an alternative route into the city centre to the M8, will see a substantial drop in traffic.

In some areas, like Govanhill, planners admit there will be little difference in traffic levels. But will M74C bring more cars to city roads? The overall impact, say backers, is for quieter local roads and as many as 700 fewer accidents over 20 years.

Greens aren't so sure: they think any new road will bring more cars and more traffic in the long run Even Transport Scotland, the agency in charge of trunk roads and, ultimately, the project, admits overall traffic will rise: but by no more, it says, than a fifth of one percent.

ENVIRONMENT THE man who was officially asked to look into the pros and cons of the M74C was sceptical about regeneration and jobs. And the environment too.

"The policy in support of environmental justice would be breached by the proposed road," said planning reporter Mr Rickman in his final report. "Those living along the route would suffer from the adverse environmental impacts, with little benefit, while the main advantages of the new road would accrue to non-resident vehicle users passing along the new motorway, and to businesses located mainly outwith the area."

Backers aren't so sure. They believe the road - despite its obviously complex and often contradictory impact - will actually have environmental advantages as well as some fairly obvious disadvantages.

"I am not a scientist," said Ms Sawers. "But I thought cars produced more emissions when they were stuck in traffic than when they were moving."

Transport Scotland too believes there will be an overall improvement in Glasgow's air quality because of the road. However, emissions of carbon dioxide, the main greenhouse gas behind global warming, would rise, Mr Rickman reported.

Over 20 years the M74C could account for an increase in C02 emissions of 138,000 tonnes or around 5.9%. On the other hand, the road will cover up some of the worst contaminated land in Scotland and clear derelict sites. It will also cut noise pollution for most Glaswegians.

TRANSPORT LINKS FOR years the campaign for the M74C was led by the head of BAA Scotland, the firm that owns Glasgow Airport. It's easy to see why. Airlines regularly cite problems on the Kingston Bridge when explaining why they choose not to fly to and from Glasgow. For some aviation executives, the transport links to the airport have proved a deal-breaker.

Finishing what is effectively Glasgow's ring road has long been a major strategic transport aim. First envisaged in 1945, the city's motorway network was always planned as part of a wider transport system combined with air and rail hubs.

Glasgow Airport has suffered from poor access links more than most businesses. The terminal, just off the M8, is on course to get a new rail link, for £210m. But the trains will only go to the city centre and most passengers will continue to use the motorway to access Scotland's biggest airport.

Privately airport executives admit they lose business because of the Kingston Bridge. The perception, said one, is worse than the reality. A small proportion of passengers worry about missing flights and book from Edinburgh or Prestwick instead of Glasgow.

The executive said he believed the M74C would swing about 2% of passengers back to Glasgow.

The M74C will also bring the eurofreight rail hub closer to central Glasgow than ever before. The terminal, at Mossend, near Coatbridge, for example, will be six minutes closer to, say, Glasgow Airport and the businesses clustered around it.

The M74 itself is now a motorway all the way to the English border. There are motorways or dual carriageways to Edinburgh and Stirling. Glasgow's roads enthusiasts seem satisfied they won't need any new motorways.

The M74C, they say, really was the missing link and not an excuse for what would be a highly controversial new problem of highway building.

1945-2011:History of a road to nowhere

March 1945: First proposal for a Glasgow motorway inner ring road, with south-eastern connection similar to proposed M74 completion, although routed through Glasgow Green rather than Govanhill.

1968-1972 M8 is ploughed through Glasgow, effectively destroying historic Charing Cross and several other neighbourhoods. Horrified residents fear the same insensitivity on the south side with long-planned inner ring road. By end of 1970s planners, facing protests and big relocation costs for businesses on the route, drop scheme. Only a half-finished off-ramp from Kingston Bridge remains of proposed road.

1988-1994 Strathclyde Regional Council tries to resurrect project. Scottish Office agrees to fund a short stretch, taking M74 into Carmyle in east end of Glasgow, sparking major local industrial development but leaving a five-mile "missing link" in Scotland's road network.

January 2001 First Minister Donald Dewar bows to pressure after three-year campaign by business and political groups to "Complete to Compete". Transport Minister Wendy Alexander calls for road, then priced at £270m, to be finished by 2007.

April 2003: A month ahead of Holyrood elections, Labour-led Scottish Executive gives formal backing to M74 project, at an official bill of between £375m and £500m. Work was scheduled to begin in autumn 2004 for completion in 2008.

December 2003: Public inquiry into project begins, after objections from businesses along proposed route.

March 2005: Public inquiry finds that the road would have no "net" economic benefit but substantial environmental drawbacks. Ministers rejected its findings and order that the road should go ahead regardless. The Herald reveals that £40m had already been spent on relocating businesses even before ministers announced results of the inquiry. Final relocation bill hits £180m.

March 2005: Transport Minister Nicol Stephen rejects findings of public inquiry and orders project to go ahead.

May 2005 Green groups launch a legal bid to halt project and drop it in

June 2006: Delay added at least £20m to cost of project.

October 2006: In a huge embarrassment for the Scottish Executive, just one bidder emerges for the right to build the road. Interlink M74 is a joint venture of Balfour Beatty, Morgan Est, Morrison Construction and Sir Robert McAlpine.

November 2007: Interlink M74 makes formal bid amid considerable secrecy. Administration holds behind-the-scenes talks to reduce costs.

January 13, 2008: Date by which the Scottish Government and Interlink M74 must sign a construction deal.

2011 Official M74 completion date.