Tunnels and Viaducts on the A90 Motorway in Italy, by Kilometre Point

The record table

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

How this table is compiled

The table on this page runs to 43 rows and records Tunnel / Viaduct, Inner Ring Road, Exterior Ring Road and Notes for each of them, which is the shape the original compiler chose rather than one imposed here. Tunnel building in Italy is shaped by geology and settlement pattern as much as by transport policy.

The inner ring road column names 19 distinct entries on this page, 150 m and 355 m among them, each traceable to the operator or administration record it was taken from. Bridge and tunnel appear on the same route more often than either appears alone, because the terrain that requires one usually requires the other.

27 of the 43 rows carry an entry in the notes column — 63 per cent of the table — and that column is where the qualifications live: tube counts, closures, boundaries and the reason a figure reads the way it does. The Faroese crossings connect islands that had no fixed link at all within living memory.

The material on this page is held in 15 captions rather than in running text, 188 words of it, each written against the image or row it belongs to by the compiler who put the page together. The kilometre point is recorded for each structure on the A90, which is how the operator identifies it.

They are not uniform: the fullest runs to 21 words and the briefest to 7, and on a page of this kind the long ones are where the explanation lives — the caption carries what the picture cannot. A crossing whose two carriageways differ in length is recorded once per direction rather than once per crossing.

Reading the figures

A tunnel list for Italy reads differently from a neighbouring country's, because the same journey time can be bought with one long bore in one country and a dozen short ones in another. De-icing is a portal problem rather than a tunnel one: the bore stays above freezing long after the approach road does not.

The note column places the route in Latium, and the administrative area is recorded because a section is identified by it. Italian motorway inventories list tunnels and viaducts together in running order along the A90. A disused tunnel is expensive to fill and cheap to seal, which is why so many survive behind a wall.

Widening an existing bore is rarely economic, so capacity is usually added by driving a second one alongside. Escape and rescue provision has driven most of the change in tunnel design over the past three decades. Ventilation type is recorded where known, because it constrains how long a bore can be built without intermediate shafts.

A pilot bore driven ahead of the main tunnel buys knowledge of the ground and is often kept afterwards as the escape route. Nineteenth-century tunnels were surveyed from the surface with theodolites and chains, and the best of them met within centimetres. Toll plazas sit outside portals rather than inside them, for ventilation reasons as much as for traffic ones.

An avalanche gallery is not a tunnel in the usual sense: it is a roof over a road, open on one side. Alpine countries dominate the rail column and coastal ones the subsea column, and neither is an accident of compilation. Smoke behaves differently on a gradient, and the uphill portal of a burning tunnel is the dangerous one.