Completed in August 1993, the St. James Interchange flyovers provide a direct connection between the M8 motorway and A737 trunk road near Paisley. Built to ease traffic congestion and permit the expansion of Glasgow Airport, the structures remain a key part of the motorway system.
The £36 million project, one of the largest undertaken in Scotland in the early 1990s, was promoted jointly by the Scottish Office and Strathclyde Regional Council.
(J28a - 29)
Scott Wilson Kirkpatrick
Planning and Design
By the 1980s, St. James Roundabout, one of the most important junctions on the M8 motorway, was suffering from disruptive traffic congestion. During peak periods it was not uncommon for traffic to back up onto the motorway creating serious safety hazards. The installation of traffic lights in the middle of the decade brought some relief, however the completion of the A737 Johnstone-Howwood Bypass, the expansion of Glasgow Airport and new developments in Paisley meant that a considerable amount of additional traffic would be using this key point on the strategic road network in the years ahead.
The Scottish Office, through Strathclyde Regional Council, commissioned a study to consider potential improvements to the interchange. It was recommended that direct links from the A737 to the M8 bypassing the existing roundabout be constructed. This was in line with recommendations made for the junction in the Greater Glasgow Transportation Study of 1968.
The Scottish Office approved the project in 1989, at which time it was decided to promote the scheme as a fixed price, design and build competition. Thirteen firms expressed interest, six of which were interviewed in December of that year. Three consortia were then invited to tender. Contract documents were issued in May 1990 with tenders to be returned by January 1991. A specimen design and specification prepared by Strathclyde Regional Council was used as the basis for pricing the project.
In April 1991 Balfour Beatty and their designer Scott Wilson Kirkpatrick were awarded the contract. Design work commenced immediately and was completed in the autumn.
The construction contract was awarded to Balfour Beatty in April 1991. Construction began in September and by early 1992 was well underway. Scott Wilson Kirkpatrick was involved in the project as main designer.
The design envisaged two multi-span viaducts, one for westbound traffic and the other for eastbound. Poor ground conditions and a need to keep costs low meant options utilising post tensioned or prestressed concrete were discounted. Steelwork was considered the obvious choice, though a box girder solution was eliminated due to the anticipated fabrications costs. Ultimately it was concluded that composite structures comprised of steel plate girders and reinforced concrete decks offered the best solution. It was a requirement of the contract that an aesthetically pleasing solution be constructed and this had an influence on the span arrangements for each viaduct. Span lengths of 50m were adopted ensuring obstacles including a busy live railway line, the M8 motorway and the local road network could be crossed with ease.
Steelwork erection proceeded at pace and involved multiple lifts. Installation of the spans above the M8 motorway posed a particular challenge and required a closure of the road.
The eastbound viaduct was designed with an overall length of 790m across sixteen spans. The westbound structure is 740m long and has fifteen spans. Each viaduct is 12m wide with carriageways of 10m. Plate girders are a constant 2.1m deep with spacings of around 3m between them. Each viaduct is curved in plan with gradients of up to 4% and a maximum height above ground of 15m. It was proposed that all steelwork be painted in a graphite coloured paint and this was approved by the Royal Fine Art Commission for Scotland. High containment parapets were included along the full length of each structure.
In addition to the construction of the two viaducts, the project also involved the remodelling of the local road network and the installation of new sign gantries, lighting and safety barriers.
Construction work commenced in September 1991 near the centre of each viaduct. Works involving the diversion of utilities and remodelling of football pitches in St. James Park were completed in advance of this date and a footbridge over the M8 at Glasgow Airport was also demolished. Erection of the steelwork, supplied by Fairfield Mabey, progressed in each direction with deck slab construction commencing when a sufficient length had been completed. The deck cantilevers and copes were constructed later in the project. The construction of each viaduct proceeded quickly and there were few problems on site. Problems with ground conditions required the installation of 25% more piles than anticipated but this had a small impact on the overall construction programme.
Construction had to be undertaken with minimal disruption to the substantial traffic flows passing through the site with carriageway closures for the installation of steelwork limited to overnights where possible. Works to remodel the adjacent roads system, including modifications to the layout around Junction 28 and Glasgow Airport were undertaken in parallel. In all, the contract saw the construction of 6km of new carriageway and required more than 4,000 tonnes of steel, 35,000 tonnes of concrete and more than 3km of new safety barrier. Other works included the installation of Glasgow type overhead sign gantries and CCTV masts as part of an expansion of the CITRAC traffic control system.
The viaducts were officially opened on Tuesday 17th August 1993 at a ceremony attended by Lord Fraser of Carmyllie of the Scottish Office and Councillor Malcolm Waugh of Strathclyde Regional Council. The project, which was joint funded by the Scottish Office, Strathclyde Region and the European Regional Development fund cost £36 million, equivalent to more than £75 million today.
On completion the project eliminated congestion from the St. James Roundabout. Thirty years on they remain a key link in the west of Scotland’s road system and a important link between Ayrshire, Renfrewshire and Glasgow. The project remains one of the most impressive motorway junction improvements undertaken in the UK, with it approved, designed and constructed in less than five years.
From the Archive
This article was first published in August 2023.