Prior to 1924, there were two main roads used between Edinburgh and Glasgow:
- The northern route, the A8, went from the West End of Edinburgh's New Town, through Newbridge, Broxburn, Uphall, Bathgate, Armadale, Airdrie and Coatbridge - originally A8, now mainly A89 and A899.
- The southern route from the West Port of Edinburgh's Old Town, through Calder, Livingston, Whitburn, Harthill, Kirk o' Shotts, Newhouse, Mossend, and Bellshill. Originally numbered as A71 to Mid Calder and A705 through to Bellshill - it's now A71, unclassified (through Livingston New Town), A705, B7066, and A775.
In 1924, the Scottish Ministry of Transport announced plans to build a new high-speed link for motor vehicles between Glasgow and Edinburgh. The route was principally planned as an unemployment relief project, and consequently it was largely constructed as single carriageway, and re-used portions of existing roads. However, approximately 37 miles was of new construction, mostly on a new alignment suitable for eventual development as a high speed dual carriageway. Initially, 4 miles were constructed with two 30-feet wide carriageways separated by a grass plot and the remainder as a single 30-feet wide carriageway with earthworks prepared for later duplication. The pavement generally consisted of a Telford base with an asphaltic wearing course, however several short lengths over boggy ground were provided with a reinforced concrete pavement.1 The western section between Glasgow and Newhouse was the highest quality build of the entire project, and explains why up to 2017, there was a gap in the M8 between junctions 6 and 7.
The 1924 route of the Edinburgh-Glasgow Road followed the historical northern route, the original A8, from Edinburgh to near Bathgate, with by-passes for Newbridge, Broxburn and Uphall. From just east of Bathgate, it took a completely new line to the southwest, joining the old A705 to the west of Whitburn. It then followed the historical southern route through to Newhouse (A73 junction),passing straight through Harthill, but bypassing Salsborough. West of Newhouse, a new line was again taken, this time to the NW, crossing the old A8 west of Coatbridge and finishing at the junction with the A80 in Glasgow.
Because the project was an unemployment relief scheme, with no definitive end date, it was plagued with delays, principally over arrangements to cross the numerous railways radiating from Glasgow. Although most of the road was drivable by 1930, it was not completely usable end to end until late 1932. By about 1930, the new road had been numbered as A8, with the A89 number used for the former A8 west from Bathgate. The A705 had been reduced to a fraction of its former length and the section of former A705 west of Newhouse was renumbered as A775. Yet, the Ordnance Survey 1932 ten mile, published before the road was entirely complete, continued to show the old road via Bathgate as the A8, with the new parts of the Glasgow - Edinburgh Road un-numbered.
The total cost of the road, including resumption of the 100 to 120 feet wide reservation, was approximately £63,000 per mile.1
Further detail about the full road project can be found at Edinburgh - Glasgow New Road.
What was once state-of-the-art in terms of alignment and construction became outdated as traffic volumes grew exponentially following World War 2. The concept of the M8 was developed to once again remove through traffic from the existing Glasgow-Edinburgh road. Parts of the M8 use the 1930s alignment, however much is built on a new route.
The first section of A8 to be replaced was the section between Newhouse and Whitburn, where it ended at a temporary terminal. Part of the road near Kirk of Shotts was an on-line upgrade of the A8. When the M8 was extended east from the temporary terminus at Whitburn, the southern half of the B7002 road joining East Whitburn and Bathgate was cut, and a new road was built to replace it and to serve a junction on the new motorway. This road ran from a T-junction on the A705, through M8 J4, to a new roundabout on the A8 Edinburgh-Glasgow Road (with the old B7002 continuing north from the roundabout to Bathgate). The new link road was numbered as A7002. Where the M8 motorway was opened parallel to the A8, the A8 was again redesignated: The A89 number was already following the original line of the A8 west of Bathgate, so it was natural that this number should be extended east from Bathgate to Newbridge. The option of reinstating the A705 number on the southern Edinburgh-Glasgow route wouldn't have been seriously considered - the road today still doesn't carry enough traffic to justify an A number, and the hill road at Kirk o' Shotts is a different route anyway, the motorway taking the original line of the A705. There was also the question of the section built new between Bathgate and Whitburn, and which had only ever carried the A8 number. A part had to be retained as an A-class road to serve the economic centre of the district, the BMC Works at Bathgate. As a compromise,the former A8 Edinburgh-Glasgow Road west of the A89 junction at Bathgate was renumbered as A7066 to the new A7002/B7002 roundabout, and beyond as B7066 through to Newhouse. Note the meeting of the A7002 and B7002, and the A7066 and B7066 at the one roundabout! Is there anywhere else where two sets of A and B pairings have met like this?
With the new M8 and M9 motorways, a new high speed general-purpose road was planned to link them through West Lothian. The A706 still continued north from Whitburn, running roughly NE through Armadale and Linlithgow to Bo'ness. The road NW from Bathgate to Falkirk was numbered as A800 as far as the A706, and as A801 only beyond the A706 (across the River Avon to Polmont and Falkirk). The new high-speed road would effectively replace both the A706 and the A800/A801. Two miles of the new road were built around 1970, linking the A801 directly to the new M9 motorway, avoiding Polmont. In the mid-1980s, a further 3.5 miles of new road was built northwards from the A7002 roundabout to a point on the A706 just short of the Avon Gorge. The earthworks continue nearly a mile further, right to the edge of the Gorge, but funding was withdrawn before the bridge could be started. Even with a couple of miles of the new road still to be completed, the A801 number was extended south along the new stretch of road, and along the A7002 to the A705. After less than 20 years, the A7002 number was consigned to history. When the A801 opened through to the M8, the parallel route through Armadale was downgraded to B-class. From the roundabout just north of Whitburn, the A706 was diverted eastwards along the B7066 to the roundabout on the A801. Thus the A706 was broken into two separate sections, connected by the A801, and the A7066 and B7066 were separated, only with a stretch of A706 between them.
The A8 originally ended outside Gourock Station, where most steam ferries disembarked to cross the Firth of Clyde. The road ahead was the start of the A78. After the station and ferry activity was cut back in the 1980s, the A78 was rerouted over the A742, which was by then the trunk route. The A8 was cut back to Greenock, with the old road around the coast becoming the A770, and the branch road to the station and ferry terminal became the A771.