Tunnels and Viaducts on the TEM — Tangenziale Esterna Est Milano

The record table

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

How this table is compiled

Read down the direction a1 column, the 16 values run from 39 to 1 064 with a midpoint at 76; the spread rather than the maximum is what says how uneven this set is. Metro tunnels are shallow, closely spaced and built under streets, which makes them a different engineering problem from an alpine crossing.

Read down the direction a4 column, the 16 values run from 39 to 1 032 with a midpoint at 76; the spread rather than the maximum is what says how uneven this set is. Tidal range decides how deep an estuary crossing must sit, and it varies more between estuaries than the crossings themselves do.

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. A national administration publishes what it maintains, so a crossing that changes owner can vanish from one list and appear in another.

This page records the structures catalogued for Italy in a tunnel almanac maintained at this address since the late 1990s. The note column records 5 exits and 3 motorway connections along the route, in running order rather than by size. The fires of the late 1990s and early 2000s reshaped European tunnel safety regulation permanently.

Italian motorway inventories list tunnels and viaducts together in running order along the TEM. The kilometre point is recorded for each structure in Italy, which is how the operator identifies it. Span rather than total length is what places a bridge in a record, because the span is the engineering and the approaches are not.

Reading the figures

A crossing whose two carriageways differ in length is recorded once per direction rather than once per crossing. Tunnel building in Italy is shaped by geology and settlement pattern as much as by transport policy. Kilometre points are given where the operator publishes them, since that is how a structure is identified in the field.

Reconstruction after a fire changes the ventilation and the escape arrangement, and often the recorded length as well. Cut-and-cover is faster and cheaper where the depth allows it, and it is the reason some urban entries have no portal in the ordinary sense. Linings are inspected on a cycle measured in years and repaired in windows measured in hours.

Emergency lay-bys are spaced by regulation rather than by geometry, which is why they appear at intervals the alignment does not explain. A record list is a snapshot of what was published, and its errors are usually inherited rather than invented. Compressed-air working let shafts be sunk through water-bearing ground and cost the health of the men who did it.

Traffic signals inside a tunnel exist to stop vehicles entering behind an incident, and they are the cheapest safety system on the list. The rock a tunnel is driven through outlives the traffic forecast that justified it, which is one reason old bores are so often reused. Wind, not weight, governs the design of a long-span bridge, and the deck section is shaped in a wind tunnel before anything is cast.

A tunnel outlasts the traffic it was designed for, and most of the cost after opening is ventilation and lighting rather than structure. Longitudinal ventilation pushes air along the bore and works until the bore is long enough that the air arrives already foul. Environmental consent now takes longer than construction on many schemes, and the dates in a list rarely show it.