Tunnels are some of the world’s most expensive infrastructure projects, which can be due to a variety of reasons, some of which are more visible than others.
Naturally, the most substantial costs will be the costs of the construction equipment, such as conveyor belts, heavy construction equipment, excavators, and the mighty tunnel boring machines commonly developed specifically for the project, as well as the costs of the teams of construction workers to operate them.
However, there are also a lot of unseen costs to constructing a tunnel, particularly given that the planning process for many large tunnels can be measured in years if not decades compared to other structures.
The Stonehenge Road Tunnel was a case in point, costing over £166m up until the end of May 2024 before its cancellation in July.
A separate analysis claimed that it would cost £250,000 per metre, which would make it amongst the most expensive roads in the world on a per metre basis.
Given the substantial expenses of the planning costs alone, the later revelation of a rough breakdown of these costs provided an even greater insight into the expensive process of tunnel construction.
National Highways broke them down into four groups and it is worth exploring all four, as well as what was not covered.
Stage One – Historical Review
The first step, at a stated cost of £13,961,610.57, was a review of the decades of previous approaches taken.
Much has been written about the exact path to the planned tunnel underneath the World Heritage Site, but this puts a price on identifying the possible options and preliminary planning work.
The initial work was exploring what had been done in the past, why a tunnel had not been undertaken in the many previous attempts, what options are available at this point (including the one proposed in 2013 that was settled on in 2017) and the cost-benefit analysis of each option.
It also included the preliminary planning work, such as ecological surveys, topographical charts, and investigating the ground to ensure that priceless historic artefacts were not lost in the construction process as well as which elements would need more intensive investigation and consideration before construction starts in earnest.
It finally also includes liaising with stakeholders and setting up a public consultation to ensure that all feedback is taken on board and the process is operated in a way that not only tries to make everyone happy but also avoids potential legal challenges.
Stage Two – Schemes And Surveys
The second stage is made of three separate parts.
The first part is an evolution of the first stage, costing £33,665,750.29, and including a mix of consultations and more intensive surveying work.
The main components of this stage are designing the preliminary scheme, a more detailed consultation with a scheme plan in mind, liaising with utility companies to ensure no pipes or wires are affected and taking that feedback on board to shape the plan.
It also includes further surveying of the ground, topography and ecology to detail the potential implications.
Finally, and most crucially for Stonehenge, it includes an archaeological survey and evaluation of the potential historic implications.
The second part, at a cost of £27,664,383.47, involves the submission of planning documents, engaging with the intensive planning process and ensuring that all statutory requirements and powers are complied with fully.
It also seems to include the costs of the many separate legal challenges against the Stonehenge Tunnel.
The third and final part, at a cost of £37,017,120.52, is the procurement and development of construction documentation. This may seem like a substantial amount, but in the spirit of “measure twice, cut once”, it helps to ensure that there is no room for error once the construction process begins.
Stage Three – Advanced Site Works
The third stage, at a cost of £52,457,822.59, is the preparation of the initial construction site ready to dig, arranged alongside continued surveying, ground examination and archaeological investigation, given the sensitive nature of the site.
It also includes developing supply distribution systems such as the installation and maintenance of conveyor belts, setting up road diversions and meeting the conditions and requirements set in their planning permission.
Stage Four – Land Costs And Compensation
The final stage, at a cost of £1,463,890.72, was compensation for the survey works that had been undertaken, liaising with current landowners and paying the cost to buy the land that the tunnel will run under.
