Road Alignment Design Development - Additional Information

The purple route would connect to the existing A83 approximately 410m south of the existing A83 bridge over the Croe Water. From there, the route would head in a north-to-north-westerly direction. The first 390m of the route would be on an embankment before it changes to a viaduct and then a tunnel, emerging approximately 150m north-east of Loch Restil on the eastern side of the existing A83 road. From there, the route would continue in a northerly direction as an open section of road for approximately 580m before reconnecting to the existing A83 where it begins to drop towards Glen Kinglas. A tunnel service building would be required at the northern entrance to the tunnel to house essential infrastructure such as power, ventilation and fire suppression services.

As a result of the tunnel, the purple route would bypass the existing B828 Glen Mhor local road junction and Rest and Be Thankful Viewpoint car park. Therefore, a new junction would be required to maintain access. This would involve using a section of the existing A83 road and creating a new junction to connect the purple route (A83) and B828 Glen Mhor local road, north-east of Loch Restil. The change to the junction location would require the location of the bus stop and any turning facilities to be considered in consultation with bus services and users.

The purple route along the viaduct section will continue to cater for road cyclists as the A83 does at present. Pedestrians and cyclists will not be allowed in the tunnel; however, they can continue to use a section of the de-trunked A83 which will form the new B828 Gel Mhor local road and would be connected to the viaduct by means of a new cycleway. The majority of walkers, cyclists and wheelers would continue to use alternative paths, such as the parallel core paths within the forested area on the other side of Glen Croe or the Old Military Road. Throughout the DMRB assessment process opportunities to enhance local walking, cycling and wheeling links will continue to be considered through the Walking, Cycling and Horse-Riding Assessment and Review. Further details can be found in the Sustainable Travel section.

Plan and Profile drawings of the purple route can be viewed through the link below and the purple route can be viewed in mapping to the right of this text. Click the link below for a further plan and drawing of the purple route.  Click here to view the Purple Option Plan and Profile drawings 

Click the links below to individually display and explore datasets on the map to the right. Please zoom in to view areas of interest.

 Purple Option Centreline 

 Purple Option Alignment 

As the purple route is located away from the existing A83, temporary traffic management would only be required where the new route connects to the existing A83 at the start and end points.

The purple route has been designed to use the flatter and less vulnerable ground below the Old Military Road. However, a series of temporary working platforms would still need to be formed to construct each of the viaduct piers, accessed from a combination of the Old Military Road and a new parallel construction access track to ensure the Old Military Road can continue to be used as the local diversion of the A83 during construction of this option. These temporary working platforms would be removed once construction is finished and the land returned to its previous state, as far as possible, but parts of the parallel access track may need to remain to enable maintenance access for the structure.

Some further temporary protection measures would likely be required upstream of the working platforms and access track to protect the workforce during construction.

• The structure and tunnel can be constructed with limited impact to road users on the existing A83; however, the connections to the existing A83 will require temporary traffic management.
• The purple viaduct is located on the lower lying ground below the Old Military Road which is less steep and less susceptible to ground movement making the excavation and construction of the foundations more efficient and less complex than other options.
• The purple route bridges across the zone of highest hillside instability on the eastern side of the glen which is associated with Beinn Luibhean.
• The purple route effectively bridges over or tunnels under the many watercourses on the eastern slope of the glen, thereby reducing the need for their management.

• To construct and maintain the viaduct, access will initially need to be taken via the Old Military Road. Given the level of access required, a second parallel access track is likely to be required during construction to ensure the Old Military Road can continue to be used as the local diversion to the A83 and to ensure plant and material can continue to access the construction site.
• Viaduct supports (piers) are susceptible to future debris flows, rockfall and landslides, and will require to be protected by defence structures. Their general upkeep and replacement due to damage will likely result in high, ongoing maintenance costs for Transport Scotland, however this has been mitigated through the design development as far as practical by moving the structure further down slope into an area less susceptible to debris flows, rockfall and landslides.
• Viaducts and tunnels of this scale will require a significant amount of materials to construct particularly concrete and steel, which would need to be transported to site, with tunnels also generating a significant amount of material to be taken off site, although all options include significant engineering works with similar challenges to varying degrees.
• Tunnel equipment, such as the fire safety apparatus and ventilation equipment, will need to be checked and maintained regularly. There would therefore be the need for several night time closures a year to undertake essential maintenance and inspections, disrupting the operation of the A83 and likely requiring traffic to use the northbound diversion during these times.

The brown route would be approximately 2.4km long of which the flow shelter and catch pit would be approximately 1.37km with the catch pit and protection wall extending a further 180m to protect the road user as the road moves beyond the Beinn Luibhean slope and area of highest vulnerability.

The brown route would connect to the existing A83 approximately 230m south of the existing bridge that carries the A83 over the Croe Water, mid-way up Glen Croe. The brown route would then tie-in to the existing A83 at an existing straight section of road north of the B828 junction. As a result, it would be necessary to provide an improved junction between the brown route (A83) and the B828 Glen Mhor local road. This would involve widening the verge on the inside of the bend directly across from the B828 Glen Mhor local road junction to improve visibility of the road ahead for all road users.

Changes to the existing bus stop and turning area would be needed, as well as a new access to the Rest and Be Thankful Viewpoint car park. The brown route will continue to cater for road cyclists as the A83 does at present. The majority of walkers, cyclists and wheelers would continue to use alternative paths, such as the parallel core paths within the forested area on the other side of Glen Croe or the Old Military Road. Throughout the DMRB assessment process opportunities to enhance local walking, cycling and wheeling links will be considered through the Walking, Cycling and Horse-Riding Assessment and Review. Further details can be found in the Sustainable Travel section.

Plan and Profile drawings of the brown route can be viewed through the link below and the brown route can be viewed in mapping to the right of this text. Click the link below for a further plan and drawing of the brown route.

 Click here to view the Brown Option Plan and Profile drawings 

Click the links below to individually display and explore datasets on the map to the right. Please zoom in to view areas of interest.

 Brown Option Centreline 

  Brown Option Alignment 

As the brown route is predominantly on the existing A83 road, there will be a requirement for temporary traffic management for road users during the full construction period, which will include traffic light operation and potentially considerable periods of full closures where traffic will be diverted to the Old Military Road, which will be upgraded as part of the medium term solution. For further details on the medium term solution including measures to reduce journey times on the Old Military Road please see  here .

• This is a predominantly online option. The debris flow shelter would provide protection through the zone of highest hillside instability on the eastern side of the glen which is associated with Beinn Luibhean.

• As a predominantly online solution, it is anticipated that construction of the brown option would require temporary traffic management resulting in traffic diverting to the Old Military Road which will be upgraded as part of the medium term solution to improve its resilience and reduce journey times in advance of the long term solution.
• Due to the location of the debris flow shelter, construction would be required in an area at risk of landslides, rockfall and debris flows. This could pose a risk of delay to the works being constructed, with increased costs and construction duration.
• Provision of a debris flow shelter which facilitates appropriate management of existing watercourses and debris flows as they cross the route will require complex design and construction. Debris flows, rockfall and landslide events in future have the ability to influence and re-direct watercourses, as a result further mitigation works to ensure they are managed correctly may be required following events

The pink route would connect to the existing A83 road approximately 750m north of the existing connection between the A83 and the Old Military Road, which is used when the local diversion is in operation.

The tunnel would run to the east of the existing A83, heading north to north-west beneath the slopes of Beinn Luibhean. The route would emerge from the tunnel approximately 150m north-east of Loch Restil on the eastern side of the existing A83. The route would then continue northwards as an open section of road for approximately 580m before reconnecting to the existing A83 road as it begins to drop towards Glen Kinglas. A tunnel service building would be required at both entrances to the tunnel to house essential infrastructure such as power, ventilation and fire suppression services.

The pink route would bypass the existing B828 Glen Mhor local road junction and the Rest and Be Thankful Viewpoint car park. Therefore, a new junction would be required to maintain access. This would involve using a section of the existing A83 and creating a new junction to connect the purple route (A83) and the B828 Glen Mhor local road, north-east of Loch Restil.  The change to the junction location would require the location of the bus stop and any turning facilities to be considered in consultation with bus services and users.

Pedestrians and cyclists will not be allowed in the tunnel and therefore will be diverted to an alternative route. The majority of walkers, cyclists and wheelers would continue to use alternative paths, such as the parallel core paths within the forested area on the other side of Glen Croe or the Old Military Road. Throughout the DMRB assessment process opportunities to enhance local walking, cycling and wheeling links will continue to be considered through the Walking, Cycling and Horse-Riding Assessment and Review. Further details can be found in the Sustainable Travel section.

Plan and Profile drawings of the pink route can be viewed through the link below and the pink route can be viewed in mapping to the right of this text. Click the link below for a further plan and drawing of the pink route.  Click here to view the Pink Option Plan and Profile drawings 

Click the links below to individually display and explore datasets on the map to the right. Please zoom in to view areas of interest.

 Pink Option Centreline 

 Pink Option Alignment 

To construct the tunnel entrance at the southern end, a temporary diversion of the A83 would be required. This would include approximately 950m of realignment, starting 600m north of the existing connection between the A83 and the Old Military Road, which is used when the local diversion is in operation and ending at the bridge that carries the A83 over the Croe Water.

• The tunnel can be constructed with limited impact to road users on the existing A83; particularly though the inclusion of a short length of temporary diversion of the A83 to facilitate the construction of the southern tunnel portal.
• The pink option tunnels under the zone of highest hillside instability on the eastern side of the glen which is associated with Beinn Luibhean.
• The pink option tunnels under the many watercourses on the eastern slope of the glen, thereby reducing the need for their management.
• The pink option tunnels under the many watercourses on the eastern slope of the glen, thereby reducing the need for their management.

• Tunnels of this scale will require a significant amount of materials to construct particularly concrete and steel, which would need to be transported to site, whilst also generating a significant amount of material to be taken from site, although all options include significant engineering works with similar challenges to varying degrees.
• A tunnel will likely require 24-hour monitoring, either on-site or externally, resulting in ongoing operational costs for Transport Scotland.
• Tunnel equipment, such as the fire safety apparatus and ventilation equipment, will need to be checked and maintained regularly. There would therefore be the need for several night time closures a year to undertake essential maintenance and inspections, disrupting the operation of the A83 and likely requiring traffic to use the northbound diversion during these times.