Why do tunnels often feature ceramic tile on their interiors?

Though not every manmade tunnel is tiled, this particular surface is commonly used in underground roads and railways worldwide. This choice is backed by several practical reasons.

The primary reason for tiling tunnels is quite similar to why bathrooms use tiles: smooth ceramic tile is easy to clean. Dirt and grime don’t tend to stick to the surface; instead, they sit on top of the tile, making it easy to wash off with detergent and water. Its resistance to dirt and moisture makes it a highly durable and low-maintenance material, staying in good condition for a long time even under tough conditions.

This is especially crucial for roadway tunnels, where exhaust from passing cars creates a constant buildup of grime. Roadway salt, dirt, and fumes get trapped inside, accumulating on the walls over time. When it becomes too dirty, city workers can easily clean the tiles using high-pressure hoses or extendable brushes.

Tiles are also a great choice for tunnels because they can be arranged to fit any surface shape. In a cylindrical tunnel, for example, tiles can be individually attached to the wall and ceiling, creating a curved surface even though each tile remains flat. This is much simpler than using metal, which would require specially manufactured sheets to match the curve and fit around corners or ledges, whereas tiles naturally adjust to these irregular areas.

Tiles are also simple and affordable to replace if they become damaged or worn out. Instead of replacing a whole metal sheet, you can easily remove any broken tiles and replace them with new ones. It's also easy to spot a damaged tile from a distance, as it will have noticeable cracks. This makes repairing any tunnel damage much more straightforward before it turns into a larger issue.

Tile also serves as a great reflective surface. In tunnels, this enhances driving visibility with less need for artificial lighting. Fluorescent lights and car headlights reflect off the walls, helping light up the tunnel. While other materials may reflect light more efficiently, they don't offer the same durability.

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