Under the sea, nation to nation.
Undersea MMC follows the same idea as the land network: one multimodal corridor built to one standard, in tunnels designed for the seabed. It can carry the same services as the land corridors, passengers included. It is a separate product line from the land corridors. The services each route carries are set for that route under the standardisation policy. The method of building each route is to be determined at detailed planning.
Status: draft. Lanes and alignments are indicative.
Global map
MMC sea crossings
Water crossings are by seabed shell: factory-cast concrete sections, floated out, sunk into a trench on the seabed, joined and covered, as at the Fehmarnbelt (18 km, about 40 m deep, under construction). Where the water is too deep for a trench, the proposal is a submerged tube tethered to the seabed; none has yet been built. The method for each crossing is set at detailed planning.
| Crossing | Route | Width (km) | Water depth | Depth class |
|---|---|---|---|---|
| Río de la Plata | Colonia – Buenos Aires | ~50 | inner estuary 1–5 m[1] | Shallow |
| Tatar (Nevelskoy) Strait | Lazarev – Pogibi | 7.3 | fairway 7.2 m[2] | Shallow |
| Palk Strait | Rameswaram – Talaimannar | ~50 | 1–3 m on the shoals; max 35 m[3] | Shallow |
| Sunda Strait | Merak – Bandar Lampung | 24 | average ~20 m[4] | Shallow |
| Strait of Malacca | Malacca – Dumai | ~48 | minimum average 25 m[5] | Shallow |
| Fehmarn Belt (under construction) | Puttgarden – Rødby | 18 | immersed tunnel at ~40 m[6] | Built type |
| Øresund (in use) | Copenhagen – Malmö | 3.4 immersed | immersed tunnel[6] | Built type |
| Channel Tunnel (in use) | Calais – Folkestone | 37.9 undersea | tunnel max ~75 m[7] | Built type |
| Strait of Magellan, Primera Angostura | Punta Delgada – Bahía Azul | 3.7 (tunnel proposed in Chile’s regional plan) | not published in the sources found[25] | To be set |
| Bering Strait | Wales – Uelen | 82 | average 30–50 m; max 90 m[8] | Shallow to moderate |
| Taiwan Strait | Pingtan – Hsinchu | 126 | average 60 m; max 150 m[9] | Moderate |
| La Pérouse Strait | Korsakov – Wakkanai | 43 | 51–118 m[10] | Moderate |
| Korea Strait | Fukuoka – Busan | ~200 | east channel ~110 m; west channel up to 227 m[11] | Moderate |
| Strait of Messina | Villa San Giovanni – Messina | 3.1 | sill 81–120 m[12] | Moderate |
| Gulf of Finland | Helsinki – Tallinn | ~80 | over 100 m at the deepest points[13] | Moderate |
| North Channel | Stranraer – Belfast | ~40 | Beaufort’s Dyke to 312 m; corridor north of it up to 200 m[14] | Moderate to deep |
| Cook Strait | Wellington – Picton | 22 | average 128 m; Narrows Basin 300–400 m[15] | Moderate to deep |
| Strait of Tiran | Sharm el-Sheikh – Ras Hamid | 13 | Enterprise passage 290 m; Grafton passage 73 m; Saudi side 16 m[16] | Moderate to deep |
| Bab-el-Mandeb | Dhubab – Djibouti | 26 | up to ~300 m[17] | Moderate to deep |
| Strait of Gibraltar | Tarifa – Tangier | ~28 (Camarinal Sill route) | sill ~280–300 m; tunnel to ~475 m below sea level[18] | Deep |
| Scotland – Faroe Islands (future) | Thurso – Tórshavn | ~420 | Faroe–Shetland Channel to 1,900 m; Faroe Bank Channel sill 840 m[19] | Deep |
| Faroe Islands – Iceland (future) | Tórshavn – Seyðisfjörður | ~510 | Iceland–Faroe Ridge largely under 500 m[19] | Deep |
| Mozambique Channel (future) | Angoche – Mahajanga | 419 at narrowest | to 3,292 m[20] | Deep |
| Åland Sea and Archipelago Sea | Kapellskär – Mariehamn – Turku | ~250 | Åland Sea to 301 m; Archipelago Sea mean 19 m[21] | Deep |
| Strait of Sicily (future) | Marsala – Kélibia | ~145 | max 316 m[22] | Deep |
| Riau Islands and Java Sea (future) | Singapore – Batam – Bangka – Jakarta | ~880 | Java Sea mean 46 m[24] | Shallow to moderate |
| Luzon Strait (future) | Kaohsiung – Basco – Aparri | ~250 | mean ~2,200 m; to ~4,000 m[23] | Deep |
Depth classes: shallow — within the depth of seabed shells built to date (Fehmarnbelt, about 40 m); moderate — deeper than seabed shells built to date, within the depth of bored undersea tunnels built to date (Ryfylke, Norway, 291 m below sea level); deep — beyond both; a tethered submerged tube or a deeper bored tunnel would be required. Widths are at the narrowest point or along the route named. The links from Australia to Asia, New Guinea, the Pacific and New Zealand are undersea links, set out below.
- Río de la Plata
- Nevelskoy Strait
- Palk Strait
- Sunda Strait
- Strait of Malacca / Malacca Strait Bridge
- Sund & Bælt, Fehmarnbelt facts
- Irish Sea fixed link study coverage (Channel Tunnel depth)
- Bering Strait
- Taiwan Strait
- La Perouse Strait, Britannica
- Korea Strait
- Strait of Messina sill, CNR
- ERR News, Tallinn–Helsinki tunnel
- ENR, Scotland–Northern Ireland link review
- Cook Strait
- Straits of Tiran
- Railway Gazette, Bridge of the Horns
- Strait of Gibraltar Tunnel
- Trap Føroyar, The sea around the Faroe Islands
- Mozambique Channel
- Westerlund et al. 2022, water transport through the Åland Sea
- Strait of Sicily
- Luzon Strait
- Java Sea
- Primera Angostura; Meganoticias, Strait of Magellan tunnel (3 June 2026)
Australian links — the MMA plan
The MMA plan joins Australia to Asia, New Guinea, the Pacific and New Zealand by seven undersea links. Lengths are measured along the alignments drawn in the MMA plan.
| Link | Length (km) | Method |
|---|---|---|
| Darwin – Singapore | ~3,500 | To be determined |
| Darwin – Manila | ~3,300 | To be determined |
| Port Hedland – Java | ~2,400 | To be determined |
| Darwin – Port Moresby | ~1,900 | To be determined |
| Mackay – Honiara | ~1,800 | To be determined |
| Mackay – Suva – Honiara (Pacific loop) | ~9,900 | To be determined |
| Brisbane – Auckland | ~2,300 | To be determined |
| Total | ~25,100 |