Road Tunnels in Ireland — Complete List by Length

• 3entries listed
• 4.5 kmlongest bore
• 1999–2006openings span
• 5.11 kmtotal length

The record table

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

How this table is compiled

A tunnel list for Ireland 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. Water ingress is pumped out continuously on a subaqueous crossing, and the pumps are the one system that can never be off.

One of those 3 is recorded as under construction or planned, Shannon at 0.9 km, so the count includes it while every measured figure — the range, the median, the total — describes the 2 rows carrying traffic today: an unopened bore cannot hold a record. Road tunnel lengths are measured portal to portal along the carriageway.

The entries sum to roughly 5.11 km of bore, an average of about 2.56 km each, though that average describes no actual row. A new scheme in Ireland would have to beat 4.5 km to change the head of this table, and that is the figure worth rechecking when one opens.

The shortest recorded entry is 0.61 km against 4.5 km at the top, a spread of 7.38x across the same table. The province column names 29 distinct entries on this page, Dublin and Cork among them, each traceable to the operator or administration record it was taken from.

The longest entry is Dublin Port, at 4.5 km, opened in 2006. 1 entries fall below a kilometre, short enough that portals and approaches usually decided their cost more than the bore itself. Approach viaducts are frequently longer than the crossing they lead to, and whether they count is the reason two sources disagree.

Reading the figures

Ventilation and escape provision, not bore length, drive most of the cost on modern road tunnels in Ireland. Many entries in Ireland carry a second figure for the parallel tube, added when the crossing was duplicated. Karst limestone hides voids that no borehole pattern reliably finds, which is why crossings through it carry the largest contingencies.

Tunnel building in Ireland is shaped by geology and settlement pattern as much as by transport policy. Salt water attacks reinforcement in a way fresh water does not, so subsea linings are specified to a different standard. Abandoned bores are retained in the record, because they remain part of the engineering history of a route.

The rock a tunnel is driven through outlives the traffic forecast that justified it, which is one reason old bores are so often reused. Linings are inspected on a cycle measured in years and repaired in windows measured in hours. Portal design is largely a function of avalanche and rockfall risk, not of architectural intent.

Seismic risk changes the lining rather than the alignment: a tunnel is among the safer places to be in an earthquake. Cost figures are omitted throughout, since currency, inflation and scope make them close to meaningless in comparison. Shotcrete applied at the face turned temporary support into permanent lining and changed what lengths were buildable.

Longitudinal ventilation pushes air along the bore and works until the bore is long enough that the air arrives already foul. Segmental linings arrive precast and are bolted up behind the machine, so the finished bore appears at the same rate the face advances. A record held for a decade is a long tenure in this field, and most have changed hands faster than that. Austria's north-south routes cross the main alpine chain three times, and its tunnel list is essentially that geography written down.