The Furlo Tunnel in Italy: Portals, Photographs and Setting

How this archive measures: lengths, bores, dates and ordering

How this archive is compiled

This page records the structures catalogued for Italy in a tunnel almanac maintained at this address since the late 1990s. Tunnel building in Italy is shaped by geology and settlement pattern as much as by transport policy. Reconstruction after a fire changes the ventilation and the escape arrangement, and often the recorded length as well.

The first railway tunnels were driven by hand and gunpowder, and their alignments still carry the marks of both. Rock temperature rises with depth, and on the deepest alpine crossings the working face has needed cooling before it needed lighting. The fires of the late 1990s and early 2000s reshaped European tunnel safety regulation permanently.

Ventilation shafts allow a longer bore to be built, and their absence is often what caps a tunnel's length. Transverse ventilation gives every section its own supply and extract, which is why the long two-lane crossings have a false ceiling. Linings are inspected on a cycle measured in years and repaired in windows measured in hours.

China's list grew faster in twenty years than most national lists did in a century, and its longest entries are all recent. Immersed tube construction is used where the crossing is short and the water shallow enough to dredge a trench. Two headings driven towards each other halve the programme and double the survey problem.

Toll revenue on a fixed link is usually pledged against the debt that built it, and the toll ends when the debt does. Older entries were compiled from printed sources and correspondence, not from online publication. Environmental consent now takes longer than construction on many schemes, and the dates in a list rarely show it.

Reading the figures

Tunnels built for one purpose are regularly repurposed for another, and a disused rail bore is the commonest cycleway in some countries. Fixed links change settlement patterns, so the traffic a crossing carries after ten years is not the traffic it was justified on. A referendum has stopped more alpine schemes than geology has.

A tunnel outlasts the traffic it was designed for, and most of the cost after opening is ventilation and lighting rather than structure. A short bore in a city can cost more than a long one in a mountain, because the expensive part is what sits above it. Cross-passage spacing, not bore length, is what modern safety regulation actually governs.

Route numbering changes over time, so a road reference in the table reflects the designation at the time of recording. Smoke behaves differently on a gradient, and the uphill portal of a burning tunnel is the dangerous one. Iceland's tunnels are short, recent and almost all built to replace a road that closed in winter.

Nineteenth-century tunnels were surveyed from the surface with theodolites and chains, and the best of them met within centimetres. Jet fans hung from the crown are cheap to add and are the usual retrofit when traffic outgrows the original design. The oldest crossings still in service were built before any of the design codes that now govern their maintenance.

A tunnel is funded on a traffic forecast and judged on a construction cost, and the two are rarely revisited together. A railway tunnel is sized by the loading gauge, and a bore built for one country's rolling stock can refuse another's. Norway builds more subsea road tunnels than anywhere else because its coast is deep, its islands are populated and a bridge would not reach. Metro tunnels are shallow, closely spaced and built under streets, which makes them a different engineering problem from an alpine crossing.