Conclusion and recommendation
Introduction
There are a range of factors that must be considered when recommending a preferred option for the MTS, covering operational, technical, programme and financial factors. Ultimately, these allow consideration of the options against the scheme objectives for the MTS which are:
Increase resilience of a temporary diversion route through Glen Croe by reducing the likelihood of it being closed during landslide, flooding and other incidents.
Maximise operational benefits of a temporary diversion through Glen Croe route for all vehicles by providing a route that achieves a proportionate balance of time to implement, cost and impact.
Reduce the likelihood of accidents on a temporary diversion route through Glen Croe.
The Option Assessment Summary Tables set out the assessment of the options under consideration against a wide range of factors that inform assessment against the objectives.
Assessment Against Scheme Objectives
Increase resilience of a temporary diversion route through Glen Croe by reducing the likelihood of it being closed during landslide, flooding and other incidents.
The following is noted in relation to the assessment of the options:
The OMR Interventions will increase resilience through reducing the likelihood of geohazards impacting the OMR or flooding events closing it. The OMR improvements would still be susceptible to vehicle breakdowns occurring in the shortened section where convoys will operate and breakdown support/recovery vehicle would be recommended.
- The Offline MTS bypasses the main landslide risk area on the A83 Trunk Road but is still susceptible to geohazard threat along its route including landslides, debris flows, or other geohazard events. The position of the route on the hillside may make it difficult to protect and geohazard mitigation may be required depending on the risks. Other resilience issues affecting the OMR such as flooding, or vehicle breakdowns are unlikely to be significant for the Offline MTS.
- The Single Lane Forestry Track Option, similarly to the Offline MTS, would be affected by geohazard threat including landslides, debris flows, or other geohazard events. Geohazard mitigation is not proposed as the principle of this option is it should be quicker and less costly to implement. However, this means the potential risks could be greater than the Offline MTS. The Single Lane Forestry Track Option would be susceptible to vehicle breakdowns occurring along its length as convoys will operate and breakdown support/recovery vehicle would be recommended.
The OMR Interventions provide a more resilient diversion route compared to the existing OMR, although still requires convoy working.
The Offline MTS potentially performs better than the other options, achieving improved resilience compared to the existing OMR, although the extent of this is somewhat uncertain given the geohazard risks and the position of the route on the hillside would mean mitigation could be required which has not been assessed. Operationally, the two-lane road would be resilient to breakdowns.
The Single Lane Forestry Track Option would perform more poorly than the other options when considered to be operating on its own due to the longer length of single lane operation and geohazard risks that could not be mitigated. If it is operated in conjunction with, or as an alternative to the existing OMR, then it would perform better and be more certain to improve resilience.
Maximise operational benefits of a temporary diversion through Glen Croe route for all vehicles by providing a route that achieves a proportionate balance of time to implement, cost and impact.
The Assessment Summary Tables contain information that considers the challenges and resulting impacts of the options across a range of factors. The assessments also consider programme and costs. Overall, the scheme objective is clear: that a balance across these is sought. This is particularly relevant as the MTS was conceived as part of the overall strategy to provide a more resilient diversion route until the Long-term Solution to the problems at the RABT is in place.
The following is noted in relation to the assessment of the options:
The OMR Interventions are smaller scale, discrete improvements in comparison to the other options, so the technical engineering, environmental and constructability impacts of the scheme are less significant than the other options overall. The journey times expected are slightly less than the existing OMR due to the slightly longer length of two-lane operation. It is significantly less costly than the Offline MTS but slightly more costly than the Single Lane Forestry Track to implement. It would be the quickest to implement, but the need for third party land and other factors may increase this duration. It is not certain whether an Environmental Impact Assessment Report (EIAR) would be necessary, but there will be environmental considerations that need addressed.
- The scale of the Offline MTS and its position on the hillside results in a complex engineering solution in terms of its design and construction. It also means that potentially significant environmental impacts would occur, particularly across areas such as biodiversity, fauna and flora, water environment and landscape and visual. An EIAR would likely be required to support promotion of the scheme due to the potential environmental impacts. Also, whilst predominantly within land owned by the Scottish Ministers, there may be some third-party land requirements at the north-western end where it joins the B828 Glen Mhor local road and then follows the route of the B828 Glen Mhor local road back to the A83 Trunk Road. It would create a two-lane diversion route and would therefore provide the shortest journey times of all of the options when in use, and in comparison to the existing OMR. The Offline MTS is the costliest of the options and it is expected to take the longest time to implement.
- The Single Lane Forestry Track Option, whilst narrower in width than the Offline MTS and following to an extent the existing Glen Croe Lower Forestry Track, is still a significant upgrade of that track along the southern slopes of Glen Croe. As such, it presents similar challenges to the Offline MTS in some areas with potential impacts, particularly around the complexity of the design, logistics around construction and environmental impacts. An EIAR is considered likely to be required in order to promote the scheme due to the potential environmental impacts. The journey times on the Single Lane Forestry Track Option are generally the longest of all the options, if it is operated on its own, and also longer than the existing OMR. It is possible that certain eastbound journeys would be quicker than the OMR interventions if it operates in conjunction with the OMR in a loop arrangement as this arrangement requires additional convoy resource, which in certain times reduces the intervals between successive convoys leaving. The Single Lane Forestry Track Option would be relatively quick to complete but would take longer than the OMR Interventions if there were no barriers to the progress of the OMR Interventions.
There is some uncertainty regarding the time to implement for the OMR Interventions as it requires third party land, which may require a statutory process to secure, adding time to the period needed for its implementation. If that additional time is not necessary, then it is the quickest to implement, is of relatively lower cost and would have the least impacts overall across the range of criteria assessed.
The Offline MTS potentially has the poorest balance of time to implement, cost and impact as it is the most complex, would have greatest impacts, cost the most and take the longest to implement.
The Single Lane Forestry Track Option is the least costly overall and may provide more certainty regarding delivery timescale given it does not involve extensive third-party land. However, environmental considerations could lead to an EIAR being required, impacting programme. The option also has numerous technical complexities and challenges that would need addressed. Journey time benefits would not be delivered unless it operated in conjunction with the OMR, and without that the journey time would be the longest of all the options.
Reduce the likelihood of accidents on a temporary diversion route through Glen Croe.
All options should be relatively safe for use as a temporary diversion route:
The OMR Interventions does have steep and narrow sections at the western end but will operate under convoy, mitigating safety risks.
- The Offline MTS provides a relatively high standard of route, but the long, steep downhill nature of the route in the eastbound direction would create some safety risks in the event of excessive speed or loss of control type incidents.
- The Single Lane Forestry Track Option has similarly a long, steep downhill nature in the eastbound direction, but operating under convoy would mitigate this.
- All options will include lengths of safety barrier due to the risks associated with the options being on steep hillsides.
Overall, all the options would be expected to have improved levels of safety compared to the existing OMR.
Comparative Assessment
With regard to the Offline MTS, whilst it would provide improved resilience and the shortest journey times, its impact, cost and time to complete make it difficult to justify as a temporary diversion only intended to operate until the LTS is in place.
The Single Lane Forestry Track Option, without any mitigation against geohazard risks, would potentially be liable to closure due to the type of landslip events of which there is evidence on the existing forestry tracks. It would not provide improved journey times if operated on its own and the journey times are not markedly improved compared to the existing OMR, even when operating in conjunction with the OMR in a loop. It would offer a reduced journey time for eastbound traffic, compared to the existing OMR, but there would be no benefit for traffic travelling westbound. The route would provide added resilience if it operated in conjunction with the OMR, with either route providing an alternative should the other be closed for any reason. Under that situation the journey times along the Single Lane Forestry Track Option would be much longer than on the existing OMR, although less than the standard diversion route along the A82/A815/A819. Continued operation of the OMR to secure the potential benefits would require the ongoing agreement of the owner of the track.
When considering the potential impacts of the Single Lane Forestry Track Option along with the resilience, journey time and other factors, it is difficult to justify as a temporary diversion. If it could operate in a loop with the OMR, the benefits in journey times are not gained by all traffic. The added resilience gained in this situation by having two diversion routes, with one continuing to operate if the other is closed, already exists with the standard diversion route, although it is accepted that the standard diversion route has longer journey times than the Single Lane Forestry Track Option. Notwithstanding this, the benefit in journey times is not significant for all traffic and any potential benefits of the Single Lane Forestry Track Option do not justify the cost and impact of providing it. The main benefit of the Single Lane Forestry Track Option would be as a diversion route if the existing OMR was not available at all and then it would provide benefits over the standard diversion route in terms of journey time.
With regard to the OMR Interventions, although it cannot be guaranteed that it would never be subject to closures, as is also the case for the other options, the proposed interventions would improve the resilience of the route as a temporary diversion. The journey time reductions compared to the existing OMR are not significant, but there is some improvement. Although not the lowest cost option, it is not significantly more costly than the Single Lane Forestry Track Option. It is also the option that could potentially be delivered the most quickly, although this would depend in particular on the ability to secure the land or rights needed to construct the improvements without significant delay. On this aspect, the OMR at its eastern end is within land owned by the Scottish Ministers. Of all the options under consideration, it is considered this presents the most appropriate option for the MTS.
Relationship of the Medium-term Solution to the Long-term Solution
Any proposal for a MTS also must be cognisant of its relationship to the LTS. There are a range of factors that are important to consider: impacts on the ability to design and construct the LTS in a way that provides the long-term resilient alternative to the existing A83; that cumulative environmental impacts are considered and managed appropriately; and value for money overall as part of the strategy for the corridor.
The OMR Interventions would be capable of being used by traffic during construction of any of the LTS options. For those options that are along or close to the existing A83 Trunk Road, there may be a need to use the OMR as a diversion route if the A83 Trunk Road is closed due to the LTS being constructed, which can happen from time-to-time on major road projects, such as when tie-ins are being built or if there are bridgeworks ongoing. Also, there may be a need for the OMR to be used by construction traffic in some situations. Neither of these scenarios should prevent the OMR Improvements being used as a temporary diversion route when needed, either in conjunction with other traffic or taking priority.
Conversion of the Offline MTS to the Green Option for the LTS would be complex but is likely to be manageable, although it is possible that some full / lane closures would be required at times. Otherwise, the Offline MTS does not interact with the other LTS options.
Conversion of the Single Lane Forestry Track Option to the Green Option for the LTS would not be possible due to the difference in the alignments and levels between the options. Otherwise, the Single Lane Forestry Track Option does not interact with the other LTS options.
There is the potential for cumulative environmental impacts to occur due to the construction of the MTS and LTS options at different locations within Glen Croe. If the MTS Offline or Single Lane Forestry Track Options are taken forward and the Green Option is provided for the LTS, the cumulative impacts would be related to the multiple constructions occurring along the same general line, leading to a cumulation of effects. In either situation, it is preferable to avoid or reduce the potential impacts, and where this is not possible, to mitigate them. In the case of mitigation, it is expected that this would be dealt with by the LTS as the extent of any cumulative impacts would only be known once that preferred option is chosen and the design progressed and assessed.
The fact sheets within this report provide an assessment of advantages and disadvantages associated with phased implementation of the MTS and LTS, assuming the Offline MTS and Green Option for the LTS. This aimed to establish the feasibility of phased implementation of the MTS and LTS. No other MTS option would facilitate this phased approach. As indicated above, this conversion would be complex to implement. Also, the assessments found that it would be unlikely to result in any cost saving. As such, it is not considered that this would change the overall assessment that it is difficult to justify the Offline MTS as a temporary diversion only intended to operate until the LTS is in place.
There is no overall benefit in relation to the Single Lane Forestry Track Option when considering the implications of the MTS and LTS as a strategy for the corridor that would change the overall assessment that it is difficult to justify the Single Lane Forestry Track Option as a temporary diversion.
Risks
Key risks relating to the OMR Interventions include:
Geohazard risks – the OMR Interventions will provide further resilience against geohazard risks. At the extreme end of the scale, in 2021 there was report of potentially up to 100,000 tonnes of material on the move on Beinn Luibhean. If there was a catastrophic failure of the hillside this would likely affect the OMR in addition to the A83 Trunk Road. There are extensive monitoring and management procedures in place to ensure the protection of road users and the workforce at the A83 Trunk Road. If such a hillside failure occurred, the standard diversion route would be available.
- Land acquisition – as the OMR is partly owned by parties other than the Scottish Ministers, acquisition of land or reaching agreement on the use of land would be necessary to implement some of the OMR Interventions. Management of any risks relating to the use of the OMR would be necessary and also for avoiding delays to the programme for completing all of the interventions, although any works within land owned by the Scottish Ministers may be able to proceed without delay.
- EIAR – the MTS design solution should aim to avoid potentially significant impacts, thereby also reducing the likelihood of an EIAR being required. Environmental considerations will still be important, but aiming to keep potential impacts to the minimum necessary and resulting considerations to appropriate and proportionate levels will avoid lengthening the programme for completion whilst still ensuring that environmental issues are given proper attention.
Overall Recommendation
Based on the assessments undertaken, and noting that the identified risks will need to be managed adequately, the OMR Interventions is recommended as the preferred option for the MTS.