The Laerdal Tunnel in Norway: the World's Longest Road Tunnel

The record table

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

How this table is compiled

A tunnel list for Norway 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 structure renamed after an opening keeps both names in circulation, and the older one persists in the literature for years.

Laerdal is recorded in this archive at 24.51 km, opened in 2000, on the list it belongs to rather than only on this page. 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.

This page records the structures catalogued for Norway in a tunnel almanac maintained at this address since the late 1990s. Cross-border schemes need two states to fund the same hole at the same time, which is why they take decades. Some entries carry a range instead of a single value where the two carriageways differ.

Water under pressure is the single most disruptive thing a heading can meet, and it is rarely where the survey said it would be. Rack railways climb where adhesion alone cannot, and their tunnels are short, steep and unlike anything on a main line. A record is a statement about what has been published, not about what exists.

Base tunnels replaced summit routes that climbed with spirals and switchbacks, and several of those older lines are still in place above them. Approach viaducts are frequently longer than the crossing they lead to, and whether they count is the reason two sources disagree. Portal design is largely a function of avalanche and rockfall risk, not of architectural intent.

Reading the figures

Length is a proxy for terrain rather than for difficulty, and the correlation is weaker than a ranking implies. Sequential excavation takes the face in slices, which is slower per metre and far more tolerant of ground that changes. Drill-and-blast remains normal in hard rock, and dominates the Scandinavian and Alpine entries in this record.

A subaqueous crossing is designed from the rock cover at the lowest point upward, and everything else follows from that number. Salt water attacks reinforcement in a way fresh water does not, so subsea linings are specified to a different standard. A record list is a snapshot of what was published, and its errors are usually inherited rather than invented.

Adding a metre to the longest tunnel in the world costs what adding a kilometre to an average one does. Two-way traffic in a single bore is the arrangement every modern regulation tries to avoid and older crossings are full of. Ventilation type is recorded where known, because it constrains how long a bore can be built without intermediate shafts.

Span rather than total length is what places a bridge in a record, because the span is the engineering and the approaches are not. The rock a tunnel is driven through outlives the traffic forecast that justified it, which is one reason old bores are so often reused. A suspension bridge carries its deck from cables in tension; a cable-stayed one carries it directly from the towers, and the two suit different spans.

Local spelling and official spelling diverge often enough that a list has to choose, and this one follows the operator. A tunnel closed for maintenance is a route severed, so single-bore crossings are worked on at night and in short windows. An avalanche gallery is not a tunnel in the usual sense: it is a roof over a road, open on one side.