Designing for Lightning Protection in Elevated Transit Structures

Elevated transit structures—viaducts, flyovers, and elevated stations—are inherently exposed to lightning strikes due to their height and isolation. A single strike can damage equipment, disrupt operations, or endanger lives. That’s why lightning protection isn’t just a precaution—it’s a critical design requirement that must be integrated from the earliest stages.

Why Elevated Structures Are High-Risk

• Increased exposure: Elevated tracks and platforms are often the tallest conductive elements in the area.

• Continuous operation: Transit systems can’t afford downtime due to lightning-induced faults.

• Sensitive electronics: SCADA, signaling, and communication systems are vulnerable to surges and electromagnetic interference.

Key Elements of a Lightning Protection System (LPS)

1. Air Termination Network
   Install air terminals (lightning rods) on rooftops, parapets, and OCS poles to intercept strikes. Use the rolling sphere method or mesh method to ensure full coverage.

2. Down Conductors
   Provide multiple, symmetrically placed down conductors to safely carry lightning current to ground. Use copper or aluminum tapes bonded to structural steel where possible.

3. Earth Termination System
   Design a low-resistance grounding system using rods, plates, or ground grids. In viaducts, integrate with pier foundations or use chemical-enhanced rods in high-resistivity soil.

4. Equipotential Bonding
   Bond all metallic elements—handrails, cable trays, OCS masts, and rebar—to the LPS to prevent dangerous potential differences during a strike.

5. Surge Protection Devices (SPDs)
   Install SPDs at power entry points, signal cabinets, and communication panels. Select devices rated for transit environments and coordinate them with upstream breakers.

6. Zoning and Shielding
   Define Lightning Protection Zones (LPZs) to protect sensitive equipment. Use shielding, cable routing, and isolation techniques to reduce electromagnetic coupling.

7. Inspection and Maintenance Access
   Include test points, inspection pits, and accessible bonding connections to support periodic testing and compliance verification.

A Field Insight

In one elevated rail corridor, lightning strikes were causing repeated failures in trackside signal cabinets. A forensic review revealed inadequate bonding and missing SPDs. After retrofitting with a full LPS—including bonded cable trays, surge arresters, and a mesh air termination system—system reliability improved dramatically, with no further lightning-related outages.

Final Thoughts

Lightning protection in elevated transit structures is about more than rods and wires—it’s about engineering resilience into the skyline. It ensures that even when nature strikes, the system stands strong, passengers stay safe, and operations continue without a hitch.