Gantry Inspection UK | Sign Gantry, Cantilever & Mast Inspection

Sign Gantry And Highway Mast Inspection

Sign and signal gantries, cantilevers and masts are highway structures in their own right, with the same general and principal inspection requirements as bridges under CS 450. They are also steel structures exposed to traffic spray, often built from hollow sections that can corrode from the inside.

Updated 28 September 2026

Which Structures Are Covered

CS 450 applies to sign and signal gantries, including portal and cantilever gantries, and to masts including cantilever masts, high masts of 20 m or more, masts for monitoring equipment and CCTV, catenary lighting supports and sign or signal posts over 7 m. The structural aspects to be inspected include foundations, columns, beams, arms, structural connections and the attachments they carry, such as fixed signs and variable message signs.

Inspection Regime

Gantries and masts follow the same cycle as other highway structures: general inspections every 24 months and principal inspections every six years, with acceptance inspections at handover. Access gantries used for inspecting bridges are different; they are inspected before use in line with the Institution of Structural Engineers guidance on the operation and maintenance of bridge access gantries and runways.

What We Look For

Gantries and masts fail differently from bridges. Loads are lighter but fatigue, vibration and wind matter more, connections are critical, and much of the steel is hollow section.

Coating breakdown and corrosion at base plates, holding-down bolts and grout
Corrosion and cracking at welded connections and around access openings
Loose, missing or corroded bolts at flanged splices and sign fixings
Internal corrosion of hollow sections, measured with ultrasonic thickness testing
Condition of galvanising and paint systems, including where they meet at repairs
Damage from vehicle impact to legs, parapets and protective barriers

Hollow Sections And Internal Corrosion

CS 450 notes that the wall thickness of steel hollow sections can diminish through internal corrosion and go unnoticed, and recommends non-destructive measurement of uncorroded thickness at critical areas. On gantries and masts, the base of columns and the areas around drainage holes and access plates are the usual places to check. We use ultrasonic thickness testing to measure remaining wall thickness without opening up the section.

Access And Traffic Management

Gantries span live carriageways, so access planning drives the programme. We coordinate inspections with planned closures where possible and use IRATA rope access where it can reduce the equipment and time needed on the network.

Common Questions

How often are sign gantries inspected?

Under CS 450, sign and signal gantries have general inspections every 24 months and principal inspections every six years, in the same way as other highway structures.

Are lighting columns covered by CS 450?

CS 450 covers catenary lighting supports, high masts of 20 m or more, and sign or signal posts over 7 m. Standard lighting columns are usually managed under separate arrangements.

Why do hollow sections need thickness testing?

Hollow sections can corrode from the inside where water gets in and cannot drain, while the outside still looks sound. Ultrasonic thickness testing measures the remaining wall without cutting into the member.

Can gantries be inspected without a full carriageway closure?

Sometimes. It depends on the gantry, the inspection scope and the network operator's requirements. Rope access and working within planned closures can both reduce disruption.