Inverkeithing to Perth motorway.

The original concept for the A92 link to Kirkcaldy was that the link from M90 would be provided at Masterton (Interchange 2). When originally constructed however, Interchange 2 whilst providing a short Motorway link A823(M) to the A823 dual carriageway to Dunfermline omitted the A92 link to Kirkcaldy. Presumably the intention was that this link, involving a long length of new road to Kirkcaldy, would follow on later since that original construction incorporated a dual carriageway overbridge on the then proposed line of the A92. This was ultimately abandoned.

In the interim A92 was linked to the M90/A90 at Admiralty (Interchange 1) with the options of following either what is now the A921 or A921/B9157 to Kirkcaldy.

However, the then Scottish Development Department commissioned a new traffic study which concluded that a new route should be considered for the A92 East Fife Regional Road. This new proposal involved moving the originally proposed A92/M90 connection from Masterton (Interchange 2) to Halbeath (Interchange 3) and following an entirely new route to Kirkcaldy and Glenrothes New Town.

There is no doubt the East Fife Regional Road, as finally built, provided a better link for Cowdenbeath and Lochgelly, and possibly Glenrothes, but did leave a developing part of the coastal area with a poorer connection to M90.

The next section going north is the Cowdenbeath and Kelty by-pass. The possibility of a new road by-passing Crossgates Cowdenbeath and Kelty was first investigated in 1948-49, at that time, as a Trunk Road. In 1966 it was designated as a Special Road and Fife County Council was invited by the Scottish Development Department to prepare a detailed scheme, W. A. Fairhurst & Partners, Consulting Engineers, being appointed to design the bridges. The line chosen at this stage was almost exactly the same as the one selected in 1949, but objections resulted in alterations near each end.

The scheme went out to tender in the autumn of 1967 and work started on the 8th January, 1968 with the Contract completion date set for July 1970. Tarmac Civil Engineering Limited, the Main Contractor, had the motorway ready for use seven months ahead of this time.

The part of Fife through which the motorway runs was scarred by widespread mining and pit bings (spoil heaps), and during construction several of these bings were used to make embankments. The removal of these unsightly mounds together with the design of the vertical and horizontal curves, has resulted in an attractive stretch of roadway with an abundance of pleasant views. It must be conceded that the topography assisted the designers but nevertheless they can take considerable credit for the result.

This stage of the M90 runs for 7½ miles in a North-South direction, and is a continuation of M90 from the Forth Bridge. !t starts near the junction of the B916 (Dunfermline to Hillend) with the existing A90. It then by-passes the former traffic bottlenecks of Crossgates and Cowdenbeath before skirting the West edge of Kelty.

Inverkeithing to Perth motorway2There are two interchanges, one a high level roundabout just East of Halbeath on the Dunfermline-Crossgates road (A907) and the other a 'diamond' interchange West of Kelty on the Dollar road (B914).

From the lowest point at the South end, the motorway sweeps over a series of intermediate summits till it reaches the highest point West of Kelty, some 325 feet above the start at the south end: it then drops 155 feet towards the junction with the A90 at Lochran.

This part of the Fife coalfield has been worked off and on for centuries. The aftermath of all this activity has been that throughout the whole programme of design and construction mineral workings featured constantly, and created many difficult but interesting engineering problems.

When subsidence of shallow workings occurs the surface movements are normally much more sudden and local than those caused by deep workings, and obviously the cost of consolidation, whatever method is used , increases with depth. As a result a decision had to be taken on the best engineering compromise between completely flexible structures to accommodate ground movement and complete consolidation of the underlying strata to prevent ground movement. Being comparatively rigid structures, bridges are able to accept only small differential movements and it was therefore necessary in this project to consolidate the underlying strata to such an extent that all except very minor differential movements are avoided. On the other hand the pavement, being comparatively flexible, can absorb relatively large but gradual movement without damage and the degree of consolidation of the underlying strata required was therefore considerably less than that for the bridges.

A comprehensive site investigation and soil survey was of paramount importance to determine the exact nature of the material likely to be encountered in road and bridge work excavations. Bore holes located at intervals along the line of the road together with extra ones at bridge sites were carried to much greater depths than normal in order to locate underlying cavities or unconsolidated waste. In some instances the results were not conclusive and further bore holes were required. In the end enough information was obtained to establish the areas which would require particular care.

Because of the mineral workings a flexible pavement of lean mix concrete surfaced with hot rolled asphalt was used throughout the length of the contract. When old workings had less than 20 feet of rock cover below motorway formation level, consolidation was carried out by excavating down to the workings and then backfilling to formation level using heavy compaction equipment. This fortunately was only found to be necessary over a relatively short length to the North-East of Halbeath.

West of Kelty the general excavation revealed a seam of good quality household coal which dipped very gradually below motorway formation level and it was felt that there was a strong likelihood that this seam had been worked. The Road Research Laboratory, together with the University of Strathclyde, were asked to undertake a geophysical investigation of the area using the Earth Resistivity method. They reported that the seam - identified as the Jewel seam - had not been worked within 20 feet of formation level. However by this time the open cast section of the National Coal Board had become interested in the commercial aspect of this seam, and arrangements were made to remove it as a continuation of the motorway excavation. Seven hundred tons of coal were excavated and taken to the Lurgi Gas Plant at Westfield. The view has been expressed that the inhabitants of Kelty and surrounding districts improved on this tonnage!

Halbeath Railway Bridge carries the motorway over the main Edinburgh-Perth line. In order to minimise the work to be carried out alongside and over the railway, the design incorporated large precast concrete blocks for the abutments and wing walls and precast prestressed beams for the deck.

Excavation of cuttings and laying of embankments were carried out by large modern earthmoving equipment in a mixture of clays, sands and degenerate sandstone. All of these materials are, more or less, susceptible to weather and some delays were experienced as a result of two unusually wet springs. However, good summers followed and the overall programme was maintained.

One small pocket of running sand was encountered near the Hill of Beath, and this had to be removed and replaced by quarry waste on top of which was laid 12" of blaes (chips of reddish bituminous shale) before proceeding with normal construction.

Though the road originally had no hardshoulders, lay-bys were provided at one mile intervals throughout. Flasher type emergency warning lights were sited at lay-bys.

Inverkeithing to Perth motorway3Altogether there are nineteen bridges in the Contract, nine overbridges, four underbridges, one pedestrian overbridge, and five twin box culverts. On the advice of the Mining Consultants it was decided that all workings under bridge sites within 100 feet of construction level would be consolidated by filling the cavities with colloidal grout under pressure. The aim was that infill material would have a strength at least equal to the coal which had been removed. A ten foot grid of 5in. and sometimes 4in. diameter holes was drilled from surface level down to the cavities and into the unconsolidated waste which normally lay below. A barrier wall was then formed round the perimeter of the area to be consolidated by injecting in stages through the perimeter holes before proceeding with the injection of material into the remaining holes.

This work was carried out at six bridge sites and involved a total drilled length of almost 27 miles . The total quantity of grout injected was 8,600 tons.

Seven of the bridges were designed to withstand minor ground movement associated with subsidence due to deep workings. This made it necessary to use simply supported spans and to provide facilities for jacking the deck to adjust levels. For the remainder site investigation showed that no movement was likely to occur and a more economic design was possible.

A basic standardisation of the appearance of all the overbridges, except the footbridge, was achieved by using similar shaped piers, deck edge beams and parapet railings. Variations occur at Duloch Bridge which has a varying depth deck edge profile, and at Calais Muir Bridge which is hogged in elevation.

A box design was used for the three underbridges at the Northern end with wing walls at varying angles to suit the locations.

The five culverts, for reasons of economy, have completely standardised internal dimensions - except for overall length. They take the form of a twin-box in standard 36" modules with individually tailored end sections. The joints between modules allow for a degree of articulation.

The'right of way' which crosses Calais Muir Bridge connects with the former Queensferry to Perth stage coach road which runs just East of the motorway at this point.

Queen Mary's escape route from Loch Leven is believed to have been very close to the line of this motorway near its North end.

The Kinross and Milnathort by-pass carries the motorway north from Kelty and includes a ¼ mile long 35 ft (11m) deep cutting. This section of motorway was the first in Britain to be constructed using unreinforced concrete pavements. Paving was carried out to full width in a single pass using a traditional concrete train with a formed longitudinal joint off -set from the centre line.

Inverkeithing to Perth motorway4It is perhaps surprising that the M90 was initially built without hard shoulders. Instead, formations were made sufficiently wide to take shoulders if required later and emergency lay-bys at one mile intervals had been provided, although hardened verges were also incorporated in the construction. This decision was apparently made due to the lower levels of traffic anticipated, but the danger posed by drivers in difficulty being unable to reach the nearest emergency lay-by, with vehicles becoming stranded in the "slow lane", was obvious.

The hardened grass verges provided during construction of the M90 Crossgates - Cowdenbeath - Kelty-By-Pass were of limited use - they were unsuitable for heavy vehicles and road users generally did not appreciate that they might support their vehicles in the event of a breakdown. Most were likely to assume that the intention of the edge of carriageway kerbs was to keep them off the verges!

Inverkeithing to Perth motorway5The relatively high potential for accidents on M90 was clear and two accidents involving the Highways and Engineering Department were significant in the eventual re-think.

The need for the addition of hard shoulders was increasingly clear and the political pressure from Fife County Council together with general public opinion played a large part in a significant decision by the Secretary of State for Scotland. In 1973 he announced that in view of the rate of growth of traffic due to developments associated with North Sea oil, hard shoulders would be built on these early sections and would be included in future motorways.

In due course Fife County Council was invited to act as Agent Authority for this work and construction was well under way when the project became the responsibility of the new Regional Council in May 1975.

The accompanying pictures show the M90 without hard shoulders, with the original emergency lay-by provision and construction work under way.

In 1972 the Secretary of State announced his decision on the line of the route from Milnathort through to Craigend at the southern end of the Perth by-pass. This decision followed a Public Inquiry on 28 days between September and November 1971. The Reporter recommended adoption of the line proposed by the Secretary of State with some concessions to objectors which were accepted by the Secretary of State.

Progress with construction was delayed by the oil crisis in 1973 but the final section through Glen Farg between Arngask and Muirmont near Bridge of Earn was opened in August 1980.

At the Craigend interchange the M90 turned north westwards to meet the A9 whilst the M85 Perth southern by-pass continued to meet the A85. Since then, however, the A85 has been renumbered as A90, and the M85 is now also numbered M90. The Craigend junction is the most northerly major motorway interchange in the UK, and because of the topography has radii well below the recommended minima and gradients well above the recommended maxima. Construction of the interchange involved deep rock cutting (greater than 164 ft (50m) deep in places) and particular care had to be taken during blasting operations to protect a 125 year old railway tunnel.

The former M85 includes the Friarton Bridge over the River Tay. The bridge is of twin box girder sections and the start of construction was delayed because of the need to check designs against the Merrison standards.

M90. Inverkeithing to Perth motorway and M85. Perth by-pass
Statistics and options.