The railway and metro industry, particularly in the underground environment of tunnels and stations, presents a unique combination of engineering challenges: the high voltage of the third-rail power supply (600 to 750 volts DC), the risk of stray current and electrolytic corrosion of concrete structures, the confined tunnel space for heavy equipment, and the critical requirement for fire resistance and low smoke emission to protect passenger life in an enclosed underground space. Conventional metals in this environment carry both an electrical conductivity risk near the third rail and, over time, suffer corrosion from persistent tunnel moisture. Nabak Composite's FRP and GRP profiles, with full electrical insulation, low-smoke fire resistance, and light weight for installation in confined tunnel spaces, offer an engineering solution for third-rail covers, emergency escape walkways, station platforms, and signaling infrastructure.

1Why Is FRP Well Suited for Railway & Metro Applications?

2Six Key Engineering Properties for Railway & Metro

Choosing FRP for railway and metro applications rests on six complementary properties. First, full electrical insulation; the most critical property for any component near a 600 to 750 volt DC third-rail power supply. Second, fire resistance and low smoke emission (Low Smoke, Zero Halogen), a non-negotiable requirement for any material inside an underground tunnel from the standpoint of passenger life safety. Third, being non-magnetic; no interference with track circuits or sensitive signaling equipment. Fourth, chemical and corrosion resistance against tunnel moisture and stray current. Fifth, light weight for fast installation in confined, low-clearance tunnel spaces. And sixth, dimensional stability and vibration resistance from continuous train passage.

Comparing corroded metal infrastructure against a comprehensive FRP solution for metro projects

The resin choice (vinyl ester or epoxy with a flame-retardant, low-smoke, Low Smoke Zero Halogen additive) for each project is recommended by Nabak Composite's technical department based on the specific fire safety requirements of the underground tunnel and the line's safety classification.

3FRP Third-Rail Insulation Covers & Power Supply Safety

The third rail, the primary DC power supply source for metro trains on many lines, carries a hazardous voltage of between 600 and 750 volts, direct contact with which can be fatal. The third rail cover, made from an FRP composite profile, is the metro industry's standard protective layer against accidental contact by maintenance staff or foreign objects with the energized rail, owing to its full electrical insulation and high mechanical strength. This cover must simultaneously be resistant to mechanical impact, non-combustible or self-extinguishing, and have certified surface electrical resistance. In addition to the third-rail cover, insulating supports and brackets for power supply equipment and a safe inspection walkway alongside the energized rail are also key applications in this section.

FRP third-rail insulation cover and metro tunnel power supply safety infrastructure

4FRP Profiles in Tunnel Walkways & Emergency Evacuation

Along the length of a metro tunnel, the trackside walkway grating provides a continuous route for the safe movement of maintenance workers and for passenger emergency evacuation if a train stops between stations. Handrails and edge protection along the tunnel walkway, a cage ladder for emergency access to exit the tunnel to ground level, and an access platform at cross-passage doorways between two adjacent tunnels are all part of the tunnel's critical safety infrastructure, which must be simultaneously lightweight, fire-resistant, and electrically insulating.

FRP walkway grating, handrail, and emergency evacuation cage ladder in a metro tunnel

5FRP Profiles in Metro Station Platforms & Infrastructure

Metro stations see high daily footfall from thousands of passengers while also carrying sensitive power and telecommunications cabling. The platform edge, marked with the standard yellow strip, requires a slip-resistant surface with high durability under heavy foot traffic. Access covers and hatches for the cable duct beneath the platform, handrails and safety protection for station stairs and landings, and grating flooring for station technical spaces and equipment rooms are also common applications of station infrastructure.

6FRP Profiles in Signaling & Telecommunications Infrastructure

The signaling system and track circuit form the backbone of train movement safety and are highly sensitive to magnetic and electrical interference. Cable trays and cable ladders near signaling equipment must be non-magnetic and non-conductive so as not to disrupt track circuit performance — a property metal inherently lacks. Access platforms for trackside signaling cabinets, insulating supports and stands for tunnel antennas and telecommunications equipment, and protective ducting for fiber-optic and telecommunications cabling are also key FRP applications in this sensitive area.

7In-Depth Technical Analysis: Electrical Safety & Fire Resistance in Tunnels

Two primary concerns for railway and metro engineers are stray current and electrolytic corrosion and fire and smoke safety in the enclosed tunnel environment. On stray current, part of the third rail's return current can leak through the ground and adjacent reinforced concrete structures instead of the rail path, and over time cause severe electrolytic corrosion of concrete reinforcement and buried metal components — a phenomenon that is extremely costly to repair inside a deep tunnel. Using non-conductive FRP profiles for components near the rail and structure eliminates this potential stray-current pathway.

In terms of fire safety, the metro tunnel is one of the most sensitive environments for material selection because of its enclosed space and severely restricted evacuation routes; dense smoke from the combustion of unsuitable materials can completely impair passenger vision and breathing within the first minutes of an incident. LSZH (Low Smoke Zero Halogen) resins for FRP profiles, with minimal smoke density and no release of toxic halogenated gases on combustion, are designed precisely for this application. The table below compares material behavior against the most important technical criteria for metro infrastructure.

8Focus on Iran's Metro & Railway Industry

The Tehran Metro network, with more than seven operating lines and further lines under development, is Iran's largest metro network, and the Mashhad, Isfahan, Shiraz, Tabriz, and Karaj metro systems are each at various stages of operation or development. New lines under construction offer a good opportunity to use FRP profiles from the earliest stages of safety infrastructure design, while older lines undergoing renovation, owing to visible metal infrastructure corrosion after years of operation, need a gradual replacement of ladders, cable trays, and third-rail covers with FRP. The national and suburban railway network also has a similar application for power supply safety and insulation infrastructure, particularly on the electrified routes in the north and south of the country.

The Economic Advantage of FRP for Iranian Metro Operators

Maintenance and repair of underground metro infrastructure is one of the costliest operational areas of any metro line, owing to the severely limited operating window (typically only a few night hours after trains stop) and the difficulty of accessing the tunnel. Replacing corroded metal infrastructure — ladders, cable trays, handrails, and third-rail covers — with corrosion-free FRP profiles noticeably reduces the frequency of nighttime maintenance and repair; a direct saving of considerable economic importance for Iranian metro operators working with limited maintenance budgets.

9Reference Standards for Railway & Metro

10Multidisciplinary Engineering Acceptance of This Solution