Deploying fibre-duct infrastructure at minimal cost


Following the example of US cities, it is possible to build a comprehensive fibre infrastructure at low cost by installing ducting during development and construction work. By creating a neutral body that can hold the ducting in trust, and make it available to stakeholders for rent, it’s possible to overcome some of the obstacles that have prevented progress in the UK.

The problem

Opportunities to install ducting for fibre at very low cost are missed

By far the largest cost in full-fibre infrastructure deployment is digging the trenches for the duct. In comparison the cost of ducts, sub-ducts and fibre are marginal.

There is an opportunity to install ducting at much lower cost when digging is already taking place. For example when developers construct new housing or business developments, or when local authorities build new roads, upgrade, or create bus corridors. Duct could also be installed when utilities companies dig up the roads to upgrade or deploy other infrastructure.

To seize this opportunity a number of US cities have created ‘dig once’ ordinances. San Francisco for example, requires: “the installation of City-owned communications infrastructure in excavation projects where the City has determined that it is both financially feasible and consistent with the City’s long-term goals to develop the City’s communications infrastructure.” In Sandy in Oregon, Council Member Jeremy Pietzold noted that his only regret about the new conduit ordinance is that “Sandy did not have the forethought to pass it 10 years ago”.

There are obstacles to progress in the UK:

  • Local authorities are wary of undertaking a role constructing digital infrastructure, fearing that they do not have the competences to maintain and commercialise it. Developers are similarly wary, preferring to leave these questions to telecommunications operators like Openreach.
  • Dig Once requires a long-term view - it may be years before some parts of the infrastructure can be brought into use. A business case based solely on local authority requirements for communications services requires a similar long view and may struggle to marry needs with solutions.
  • More can be achieved through partnership, but local authorities worry about legal issues such as state aid. 

The solution

Making Dig Once work in the UK context with a neutral body to hold assets in trust

It is possible to get round these problems by introducing a new body:

  • To hold assets ‘in trust’ until such time as they can be brought into use;
  • To look after the administration and commercialisation of the growing network;
  • To stand as a neutral intermediary between stakeholders.

A Dig Once Duct Trust is a neutral body, charged with the creation of a shared asset and with making that asset available to carriers and service providers.

It is concerned solely with the assembly, maintenance and rental of a duct network. It does not get involved in service provision or network operations. It charges rental fees to access the ducting. Revenues are used to cover costs, including the marginal cost of duct installation in open trenches, to return a share to property owners, and for reinvestment in the network.

Such a neutral body can command the confidence of service providers and public sector partners, and potentially including utilities.

The outcome

A growing network of duct available for sharing

The word ‘trust’ is used in this document, but a variety of bodies can undertake the stewardship of such an asset, such as a CIC or mutual.

The trust body can be charged with different missions, depending on the stakeholders involved. For example duct space may be made available of purely commercial terms, or some elements may be reserved for public sector use, or limits set on the amount of asset made available to any one user.

One standard 100mm duct can be populated with sub ducts and can contain many hundreds of dark fibre pairs. This allows a diverse range of options.

The Thin Layer Model offers a way to keep part of the asset available for shared use by public sector and smaller digital and service provider businesses. Remaining capacity can then be offered in larger blocks. 

CBN and Dig Once trusts

The Dig Once trust model has been developed by CBN and is under consideration by various local authorities. CBN has been working with Tameside MBC which has been operating its own dig once policy for over 5 years: isolated sections of duct installed in the past have now come into use. The Dig Once Trust concept perfectly complements the Thin Layer Model pioneered in Tameside.


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