Castlecary Junction

The junction seen from the Viaduct

Castlecary Junction is junction 6A on the M80. It was built in the 1960s as a junction on the A80, and originally allowed six of the eight conceivable turning movements, there being no exit slip road from the NE-bound A80.

After the A80 was upgraded to motorway as the M80 in 2011, only two movements remained possible for all traffic, with a further two for buses only. The tightly curved southbound on-slip was completely removed, and "bus gates" were added to prevent traffic other than buses heading into or out of Castlecary village from/to the M80. However, a lot of traffic overcame this by simply making a U turn a little further east along the B816, and so these bus gates appear to have been removed by c2016, although painted 'Bus Only' markings on the onslip can still be read.

History

The old A80 / B816 junction with traffic island

The junction was originally a simple T-junction immediately to the north of the Viaduct, where the B816 terminated on the A80. The dualling of the A80 in the 1960s substantially changed the surviving roads, so that much of the old road lines are now buried, but some bits remain to piece together the old routes. Although the scale of old maps makes it difficult to be certain, the A80 approached from the south west along what is now the B816 and appears to have originally passed under either the first or second arch from the east end of the viaduct. It then turned eastwards again, along what is now the minor road to Walton Farm. Remarkably, the old junction still retains the traffic island, as the A80 swung northwards, and the B816 continued to the east. The original route of the B816 peters out in fields before reaching the new road line.

The old A80, however, runs north to meet the new B816, and is then severed by the offslip from the motorway. Its onward route survives however, and after a short diversion east along the B816, Cumbernauld Road (walkers and cyclists only) leads back to the old A80 line as it dips to cross the canal, before climbing up past Haggs to meet the A803 in Longcroft.

Although the 1970 1:2500 OS sheet appears to show the completed grade separated junction in its first incarnation, both the 1971 and 1974 OS One Inch Sheets show a different layout. The B816 is shown as forming a staggered crossroads across the junction, and while the overbridge is marked (as a footbridge?), the implication is that it is not available for traffic. The eastern approach is coloured yellow, and quite clearly terminates between the junction with the former A80 and the bridge. On the western side, the curve of the B816 is depicted as a track leading off the B816. To show this layout in 1971 would indicate that the junction is under construction, but to still show it 3 years later suggests that for some reason the junction was left half finished, or it could just be a mapping error.

Routes

Route	To	Notes
M80	Stirling
M80	Glasgow, Carlisle	Access only to and from M80
B816	Castlecary
B816	Bonnybridge
	Walton	Walton Road. Access only to and from B816