Existing conditions
This chapter describes the existing conditions on the existing A83 Trunk Road, the OMR, the forestry tracks on the west side of Glen Croe and the B828 Glen Mohr local road. A thorough review of the existing conditions within Glen Croe is provided within the Access to Argyll and Bute (A83), Strategic Environmental Assessment & Preliminary Engineering Services, DMRB Stage 1 Assessment Report.
A83 Trunk Road
The A83 Trunk Road is a 98-mile (158km) road in the Argyll and Bute council area providing a strategic link to Central Scotland. The route is one of only two east-west strategic trunk network connections between Argyll & Bute and the Central Belt.
The road originates at Tarbet, at its junction with the A82 Trunk Road on the western side of Loch Lomond and terminates in Campbeltown at the southern tip of the Kintyre peninsula.
The section of the A83 Trunk Road through Glen Croe, between Ardgartan and the RaBT viewpoint at the A83 Trunk Road /B828 Glen Mohr local road junction, includes the highest point along the A83 Trunk Road at approximately 265m above ordnance datum and the adjacent hillsides have a history of instability leading to landslides and road closures.
From January 2007 onwards, the A83 Trunk Road has been closed on numerous occasions due to debris flow events blocking the road or as a precautionary measure because of a high risk of a debris flow event occurring. These closures have increased in regularity in recent years due to the increasing frequency of heavy, intense periods of rainfall. Table 2.1 lists the closures from 1 January 2007 to 18 November 2021.
| Date Closed | Date Opened | Duration |
|---|---|---|
| 28-Oct-07 | 11-Nov-07 | 14 days |
| 08-Sep-09 | 10-Sep-09 | 2 days |
| 01-Dec-11 | 03-Dec-11 | 2 days |
| 22-Feb-12 | 25-Feb-12 | 3 days |
| 22-Jun-12 | 23-Jun-12 | 1.5 days |
| 01-Aug-12 | 03-Aug-12 | 2 days |
| 19-Nov-12 | 20-Nov-12 | 1 day |
| 03-Oct-13 | 04-Oct-13 | 1 day |
| 09-Jan-14 | 10-Jan-14 | 1 day |
| 06-Mar-14 | 11-Mar-14 | 5 days |
| 28-Oct-14 | 02-Nov-14 | 5 days |
| 30-Dec-15 | 01-Jan-16 | 2 days |
| 04-Jan-16 | 07-Jan-16 | 3 days |
| 09-Oct-18 | 18-Oct-18 | 9 days |
| 30-Jan-20 | 02-Feb-20 | 2.5 days |
| 04-Aug-20 | 06-Sep-20 | 33.5 days |
| 13-Sep-20 | 22-Sep-20 | 10 days |
| 19-Oct-20 | 21-Oct-20 | 3 days |
| 29-Oct-20 | 07-Jan-21 | 70 days |
| 11-Jan-21 | 12-Jan-21 | 1 day |
| 14-Feb-21 | 15-Feb-21 | 1 day |
| 18-Feb-21 | 02-Mar-21 | 12.5 days |
| 28-Mar-21 | 29-Mar-21 | 2 days |
As a result of ongoing concerns regarding the stability of the hillside, the A83 Trunk Road has frequently been closed and the OMR diversion utilised as a diversion route.
Old Military Road (OMR)
The OMR was the original road to link Dumbarton with Inveraray and was in operation until the late 1930s when improvements were carried out to form what is the A83 Trunk Road today. The road also has a rich history with Scottish motorsport because of its steep gradients and hairpin bends at the far west of the road and was used for hill climb events up until 1969. At present approximately 2.6km of the OMR is situated within land owned by a private landowner with the remaining 1.4km situated within land owned by Scottish Ministers and managed by Forestry and Land Scotland (FLS). Transport Scotland has an agreement with the landowner to use the OMR as a temporary diversion route when the A83 Trunk Road is closed.
The road is made up of a bituminous bound material. The section in Scottish Ministers ownership is largely two-way whereas the 2.6km section in private ownership is single lane, varying in road width between 3.0m and 3.5m with widening in place towards the hill climb of about 6-8m. The majority of its length is relatively level and straight beneath the A83 Trunk Road, however, the final third of the OMR rises steeply alongside winding geometry to reach the RaBT carpark at the top of the Glen.
The OMR was brought in to use as an emergency diversion route, during A83 Trunk Road closures, in 2013 following a study on the use of the OMR and the forestry tracks, located on the southwest slopes of the glen, as potential diversion routes. Due to the narrow-paved width, poor geometry and the presence of considerable hazards immediately next to the road (e.g. steep slopes), the OMR operates over part of its length under a one-way convoy system. The current journey time along the OMR is around 13 minutes with no wait time for the vehicles. This is in comparison to the normal journey time on the A83 Trunk Road from the start of the OMR to the end of the OMR heading westbound of about 2.5 minutes at a speed of 85kph.
The OMR is also at risk (albeit a lesser risk than the A83 Trunk Road) of debris flow events as it is situated directly downslope of the A83 Trunk Road. The OMR itself has had to be closed in 2020 due to debris flow events above the A83 Trunk Road reaching the OMR, stream discharges over the OMR and flooding from Croe Water. On occasions like this, when the A83 Trunk Road and OMR are both closed, traffic is diverted onto the longer pre-planned diversion route via the A82/A85/A819. Between January 2020 and December 2021, the longer diversion route was in operation on 63 days.
The most notable OMR closures were due to the significant landslide that occurred in August 2020 where 5,500 tonnes of debris dispersed down the hillside. 2,000 tonnes was collected by the landslip mitigation catch pit with 1,500 tonnes reaching the A83 Trunk Road and the remaining 2,000 tonnes continuing to the OMR. There was a secondary landslip in September 2020 that also contributed to the closures with a further 3,600 tonnes of debris blocked by the landslip mitigation fences.
Forestry Tracks
The existing forestry tracks on the southwest slopes of Glen Croe were formed into the very steep hillside generally in a cut-fill operation. The lower forestry track is approximately 3.5km in length. The track rises from approximately 91m above sea level at its eastern end to a height of approximately 292m at its western end. The track is owned by Scottish Ministers and managed by FLS and dates back around 70 years. FLS use it to access the surrounding forest, and, in the future, it will be used to access the forest for harvesting operations. The lower forestry track also forms part of a designated core path within the area.
The lower forestry track is unbound, and the alignment is changeable with variable horizontal and vertical geometry. The vertical alignment exhibits a steady climb travelling westbound with an average gradient of 6.5% but some sections are as steep as 14% in places. The average track width is 3.2m but there are localised sections as narrow as 2.6m due to erosion and downslope failures. The steep slope is separated by a soft verge ranging from as narrow as 0.2m to 6.6m with an average of 1.2m.
B828 Glen Mohr Local Road
The B828 Glen Mohr local road is the main route, from the east, to Lochgoilhead and Loch Goil. It is a single lane carriageway with narrow informal soft verges and drainage ditches. It is a local authority operated road, with winding, undulating geometry and passing places are situated approximately every 200m. The road is made up of a bound surface and from visual inspection appears to be generally in good condition.