Road Tunnels: Beneath it all

Author: Michael Vogel

Aug 03, 2022 Safety on the road / Future Vehicle & Mobility Services

They run beneath mountains, towns, or water: There’s the road tunnel with brightly lit halls, another with an undersea traffic circle, and yet another that serves as a backwater basin. We present some unusual structures.

Why climb tens of meters in altitude, first up, then down again, when you can do it in a straighter line? It is unknown who first asked themselves this question about roads. However, it is certain that the Ertruscans and Romans built tunnels in order to shorten routes in what is now Italy before the turn of the millennium. The Grotta di Pozzuoli in Naples is one example. It was built in the 1st century BC. Four meters high and four meters wide, the tunnel is inaccessible to the public today. Daylight enters the 700-meter-long connecting section through a hill not only from the ends but also through shafts from above, set roughly in the middle of the tunnel.
Although some road tunnels were built early on, more extensive construction activity in Europe did not begin until the 19th century. In 1802, for example, the first road tunnel to cross the Alps was opened – under the Colle di Tenda pass, which separates the French Maritime Alps from the Ligurian Alps. There was also a real boom in the second half of the 20th century, due to the highway network’s major expansion.
Road tunnel with a length of more than 20 kilometers
At three kilometers in length, the Colle di Tenda, or Col-de-Tende Alpine tunnel in French, was one of the longest road tunnels in the world for many years and is still passable for cars and motorcycles today. Nowadays, however, the record length for road tunnels is beyond 20 kilometers. The world’s longest is the Lærdals Tunnel near the southern Norwegian fjord coast. It measures 24.5 kilometers and went into operation in the year 2000 after five years of construction. Second place goes to the twin-tube Yamate in Tokyo with 18.2 kilometers. It was fully opened in 2015.
The Lærdals is a single-tube structure, which means there is two-way traffic in the tunnel. At the maximum speed allowed, a vehicle needs about 20 minutes to pass through – which can make you feel queasy. The slightly curved course of the tunnel is supposed to help against fatigue, and three huge, brightly lit caverns help calm anxiety. These three caves are evenly distributed over the 24 kilometers. There you can take a break, make a U-turn – or get married, which has actually happened.
Strict safety standards for road tunnels
Tunnels are fatal places when it comes to accidents, or perhaps even fires. Not least as a result of the serious accidents in the French-Italian Montblanc Tunnel and the Austrian Tauern Tunnel, which occurred within two months of each other in the spring of 1999, the EU drew up a directive. Since 2004, it has regulated the basic safety standards in the trans-European road network in order to achieve a uniform level of safety in the member states. This includes, for example, signage that must be visible even in smoke, as well as defined markings on the roadway and on walls. Beyond a certain tunnel length, emergency stops are mandatory at regular intervals. Escape routes are also mandatory: exits to the outside, cross connections between tunnel tubes, escape tunnels, or shelters.
The EU member states had 10, and in some cases 15, years to adapt the affected road tunnels to the European minimum standards. However, the tunnel tests repeatedly carried out by the German automobile club ADAC show that this has not yet happened everywhere.
Natural ventilation is sufficient in tunnels up to about 400 meters in length. Longer tunnels require a technical supply of fresh air. Modern, busy long road tunnels are equipped with smoke detectors, video surveillance, loudspeakers, and receivable traffic radio so that rescue forces or vehicle occupants can be informed quickly in the event of danger.
Norway has the longest road tunnels
The air conditioning is currently being upgraded at the Lærdals tunnel. Incidentally, it will not be the record holder for much longer, though the record remains in Norway: The Boknafjord Tunnel is under construction on the west coast, north of Stavanger. It is scheduled for completion in 2025/26. It will then measure 26.7 kilometers and run under water in long stretches. This will also make it the longest underwater road tunnel in the world. The Eysturoyartunnilin, which was opened to traffic at the end of 2020, has held this record until now. It connects the two largest of the Faroe Islands and has a length of 11.2 kilometers. It even boasts a traffic circle deep under the ocean.
Water is also a factor for the SMART tunnel in Malaysian capital Kuala Lumpur. The name SMART stands for “Stormwater Management And Road Tunnel” – which says it all. It can be used simultaneously as road tunnel and as water drain. During heavy rainfall – Malaysia is located in the tropics – any floodwater that occurs first runs into a tunnel in which the two-story traffic tube is embedded. In this case, vehicles can continue to use the tunnel. Only when extreme flooding occurs is the road tube closed to traffic and also flooded. The water tube is 9.7 kilometers long, the traffic tube four kilometers. The structure has been in full operation since 2007. So far, the traffic tube has been flooded eight times, most recently in 2021. It is unlikely to have been the last time.