Tunnel inspection robots in the UK: which robot suits which tunnel, culvert or shaft, and what the operators have found

Yes. Network Rail describes its culverts as brick or concrete tunnels about 50 to 60 metres long and 400 to 1,200 mm wide, many more than 150 years old, which usually needed the track above to be closed so staff could inspect them. It has worked with a small Unitree legged robot, known as Eric, since 2024; the robot completed its first culvert inspection under the railway in Essex on 7 February 2025, and Network Rail says it captures more detailed data without staff entering the structure and without line closures.

UK Power Networks ran an Ofgem Network Innovation Allowance project with Arup, from October 2022 to August 2024 with a £432,000 budget, deploying a four-legged robot in cable tunnels and shafts, starting near its Leicester Square substation. Images feed Arup's Loupe 360 viewer, which uses machine learning to flag degradation. UK Power Networks says it has 47 network-owned tunnels, nearly a third of those owned by distribution network operators in Great Britain, with more than 160 tunnel inspections a year, and estimates the approach could cut staff time in high-risk locations by up to 50%. National Grid's 20 km Elstree to St John's Wood cable tunnel has had a monorail with four remote-controlled inspection vehicles carrying infrared cameras since 2004. All figures are the operators' and suppliers' own, not Forge results.

These are forms, not named products. The structure's dimensions, water, silt, access points and signal decide which one fits, and a survey of the structure comes before any platform is chosen.

Confined spaces

Most tunnels, culverts and shafts meet the definition of a confined space: an enclosed place where there is a reasonably foreseeable risk from gas, lack of oxygen, rising water or similar. Under the Confined Spaces Regulations 1997 no one should enter to work unless it is not reasonably practicable to achieve the purpose without entry. Robot inspection is that avoidance for routine looking. Anyone who does enter, including to recover a stuck robot, needs the full controls. Our guide to confined space inspection robots covers the Regulations in detail.

Highway structures: CS 450

National Highways' standard CS 450, "Inspection of highway structures", sets general inspections at intervals of 24 months and principal inspections on a six-year cycle for structures within its scope, which include buried structures and culverts (road tunnels are read alongside CS 452). A principal inspection is a close examination, within touching distance, of all accessible parts of a structure, and uses techniques such as hammer tapping to detect loose concrete. CS 450 allows the inspecting agent to propose alternative means of access for areas of difficult or dangerous access, including confined spaces, for agreement with the technical approval authority, and it notes the constraints on drones under bridge decks and in confined spaces. A robot can supply visual, thermal and dimensional evidence; whether that evidence satisfies a given inspection is agreed with the overseeing organisation, not assumed.

Culverts and outfalls: CIRIA C786

CIRIA's "Culvert, screen and outfall manual" (C786) is widely used UK guidance on managing culverts, including inspection checklists. It is a useful reference for deciding what evidence an inspection must capture, and so what a robot must be able to see.

Railways and power networks

Network Rail and the electricity network operators set their own examination regimes and safety rules for their structures. Robot routes, supervision and recovery must sit inside those rules. On electricity sites, see our guide to substation inspection robots.

Lighting and a zoom camera with enough resolution to read cracks, spalling, joints, missing bricks and water ingress. A thermal camera where cables, joints and electrical fittings are part of the inspection. LiDAR where the question is deformation, silting, ovality or change between visits. A gas detector covering oxygen, flammable gas, hydrogen sulphide and carbon monoxide, because tunnels and culverts can accumulate all four. For flooded culverts, sonar on a floating or submersible platform instead. Each payload adds weight against the robot's rating and must itself be rated for wet, dirty conditions.

A tunnel or culvert inspection produces a record per structure, per section, per visit: defects, condition ratings, photographs and measurements that feed the owner's structures database or asset management system and, when something is wrong, a work order. UK Power Networks' trial shows the value of comparing each run with the history of the same location; that only works if the data is organised by structure and position, not by robot run.

Forge Anvil is the integration software we are developing for this job: carrying findings into the systems an owner already keeps. For tunnels and culverts, the pattern we would scope looks like this:

How large LiDAR and point-cloud files are handled, whether attached, referenced or kept in an existing survey system, is scoped per project in the integration review, along with which systems Forge Anvil connects to. The integration patterns are in our guide to integrating a robot with the software you already run.

Pick one structure type and one inspection: a set of culverts on a route, or one cable tunnel. Survey access, dimensions, water, silt and signal first. Choose the form from the table above, then the platform from its published ratings. Involve the structures engineer who signs the inspection, the permit and rescue owner, and whoever manages possessions or closures. Agree the measures:

Include an exit condition, for example if silt or water prevents consistent coverage. That is how we structure a pilot programme. Network operators can use Ofgem's innovation allowances, as UK Power Networks did; for other owners, grant or innovation funding can sometimes contribute towards a suitable pilot, subject to eligibility and the schemes open at the time, and is never guaranteed.