Topographical Surveys for Highways, Utilities, and Infrastructure

Two distinct specialisms

A topographical survey supports two distinct specialisms in UK infrastructure work:

1. Highways — Section 278, Section 38, Section 106 agreements under the Highways Act 1980
2. Utilities — PAS 128 underground utility detection and verification

The two are often combined on the same project but require different surveyor expertise and different deliverables.

Highways projects (S278, S38, S106)

UK highway adoption agreements are formal contracts between a developer and the local highway authority. The three main types:

• Section 278 (S278) — new estate road into existing highway. Requires topographical survey + 5m grid + 0.25m contours + kerb lines + drainage + lighting.
• Section 38 (S38) — adoption of new road. Requires topographical survey + 5m grid + 0.25m contours + drainage + lighting + traffic calming features.
• Section 106 (S106) — highway improvements as planning condition. Requires topographical survey + kerb lines + traffic calming features.

The minimum spec for highways projects is the same as a standard planning topo (RICS Band B, 5m grid, 0.5m contours) but with the addition of kerb lines, drainage features, and lighting columns.

Utility surveys (PAS 128)

PAS 128: Specification for underground utility detection, verification and location is the UK standard for utility surveys. It defines four survey types:

• PAS 128 Type D — Desktop utility record search only (no site work)
• PAS 128 Type C — Desktop + site reconnaissance for above-ground features (manholes, valves, etc.)
• PAS 128 Type B — Type C + GPR (Ground Penetrating Radar) + electromagnetic location (detect + trace)
• PAS 128 Type A — Type B + verification (excavate or slit trench to confirm a specific utility)

A typical infrastructure project needs at least Type C (for planning) and Type B (for design and construction). Type A is reserved for high-risk locations (near hospitals, schools, critical infrastructure) or where the consequences of a utility strike are severe.

Utility features to capture (Type B and above)

A PAS 128 Type B utility survey captures:

• All manhole / chamber locations + cover + invert levels
• All valve / hydrant / stop-tap locations
• All service runs (with depth where detectable via GPR)
• All utility markers / signage
• All utility trenches / ducts
• All above-ground utility features (poles, substations, cabinets)

The deliverable is a combined utility and topographical plan showing the utility features overlaid on the topographical survey base. The accuracy is stated per utility type per PAS 128 confidence level.

Delivery standard for highway/utility projects

For a typical 2026 highway/utility project, the minimum spec is:

• Topographical survey: RICS Band B, 5m grid, 0.25m contours
• Utility survey: PAS 128 Type C minimum (Type B for design)
• Combined plan: utility features overlaid on topo base
• Accuracy band stated per utility type
• Confidence level stated for each detection
• Recommendations for any Type A verification needed

The deliverable is a single combined CAD plan (DWG + PDF) that the highway engineer and the utility designer can both work from.

How to commission

The commissioning process is the same as a standard topographical survey, with three additions:

• Specify the highway agreement type (S278, S38, or S106)
• Specify the utility survey type (PAS 128 Type C or B)
• Specify the deliverable format (combined plan, separate plans, or both)

The fee premium for the highway/utility spec is typically 50-100% over a standard topographical survey of the same site (due to the additional utility survey work).

Download

Next steps

• See our Topographical Survey service page
• See Asset 1: The Complete Guide
• Book a 15-minute clarity call

References

Frequently asked questions

How long does a topographical survey take? A 1-hectare site with mixed vegetation typically takes 1 day on site for a 2-person GNSS team, plus 1-2 days for processing and drafting. Larger or more complex sites take proportionally longer.

What accuracy can I expect from a topographical survey? With modern GNSS RTK and the RICS Measured Surveys 3rd edition methodology, typical accuracies are:

• 15-20mm horizontal, 20-30mm vertical for open-sky GNSS RTK
• 2-5mm for total station work
• 20-50mm for drone photogrammetry (depending on flight height)

Do I need a topographical survey for a small extension? For a typical rear extension, a 5m-grid topographical survey at 0.¹²³25m contours is sufficient. For a side extension or a more complex site, a 2m grid may be needed.

How do I choose between GNSS, total station, and drone? Large open sites favour GNSS RTK (fast, cost-effective). Tight urban sites with kerbs and drainage favour total station (no satellite issues). Large external sites favour drone (fast coverage). For most UK 2026 projects, a mixed approach works best.

Can a topographical survey locate underground services? Not by default — that's a separate PAS 128 utility survey. A topographical survey captures only the visible utility covers, manholes, and inspection chambers. For underground service detection, a separate PAS 128 Type B or Type A utility survey is required.

What is the difference between a topographical survey and a land survey? They are essentially the same thing. "Land survey" is the older term; "topographical survey" is the modern RICS-preferred term. Both produce the same deliverable: a 2D plan with contours, spot heights, and features.

How do you integrate a topographical survey with the OS National Grid? Modern surveys use GNSS RTK with OS Net correction, applied via the OSTN15 transformation grid to convert ETRS89 satellite coordinates to OSGB36 local grid coordinates. The output is fully OS-compatible.

Can a topographical survey be done in winter? Yes, but with caveats. Frozen ground affects spot height accuracy. Snow cover obscures ground features. Heavy rain makes site access difficult. Most UK 2026 surveys are done in spring, summer, or early autumn.

How do I commission a topographical survey? The standard process: send a brief, receive a fixed-fee quote, verify surveyor credentials, arrange site access, site visit, CAD/DTM production, QA check, delivery. Most 2026 quotes are returned within 48 hours.

How to commission

Book a 15-minute clarity call with an Icelabz topographical surveyor, or read the topographical survey service page for the full service description.