Peter Kenyon and Armand van Wijck, TunnelTalk

As the official investigation into Switzerland's worst ever tunnel crash gets under way, TunnelTalk News Editor, Peter Kenyon and its Europe Corrspondent Armand van Wijck look at the relevant legislation concerning emergency lanes in European tunnels and talk to Dutch tunnel safety expert Evert Sonke.

Sierre tunnel drive-through video (2010)

In many ways Sierre's 2.6km long twin-tube traffic tunnel, in which 22 children, four teachers and both bus drivers lost their lives last week (March 2012), is remarkable only for being so unremarkable.

Built as recently as 1999, it has a modern design, complies with all existing safety regulations, is twin-tube rather than bidirectional, and in 2005 was rated by the European Tunnel Assessment Programme (EuroTAP) as having a "good" safety rating overall.

Its safety features include emergency exits every 300m, fire extinguishers and telephones every 150m, and emergency laybys every 600m. If one could pick a tunnel where Europe's second biggest tunnel disaster might happen, Sierre would not be on the list.

Additionally, driving conditions were nearly perfect on the day of the crash (March 13), traffic was light, the accident did not happen near the tunnel portal (thereby eliminating tunnel blindness as a cause), and no other vehicles were involved. This much has been verified by CCTV footage inside the tunnel.

Emergency crews at the tunnel entrance (Photo credit: EPA)

Sierre tunnel, however, was an accident waiting to happen in one crucial respect. And it is a design flaw that is almost certainly shared with many tunnels throughout the world. In short, the existence of perpendicular and unprotected walls at the ends of the emergency laybys must be considered highly dangerous.

This danger is especially relevant within the confined space of a tunnel, a danger that is heightened by the fact that only the slightest deviation to the right, if occurring at exactly the wrong time, could lead to a full-on impact with the concrete end wall. That 28 people died during the impact, despite wearing seatbelts, illustrates its severity.

The Swiss Federal Office for Roads is now examining whether the 90-degree angle of the wall increased the severity of the crash. Spokesman Michael Mueller told the Associated Press: "In principle there is the possibility of slanting the angle of the bay, or protecting it with concrete or other elements."

Perpendicular wall at end of emergency layby (Photo credit: EPA)

He added: "Such a severe and tragic accident must always be taken as an opportunity to analyse the factors that could have influenced the causes and effects of the disaster."

Olivier Elsig, prosecutor for the Swiss canton of Valais, said the cause of the crash was being investigated, but said CCTV footage showed they could "categorically exclude" the possibility of a collision with another vehicle in the unidirectional tunnel. Elsig also said initial investigations suggested the coach was not speeding above the limit of 100km/h (62mph), leaving possible causes of a technical error with the bus or the driver.

Switzerland is not a member of the European Union and is therefore exempt from meeting the minimum safety criteria laid down in the 2004 EU Tunnel Safety Directive, although the Sierre tunnel does meet all EU criteria relating to safety lanes and emergency laybys.

Map showing accident location

Swiss Federal Road Agency (OFROU) spokesman Antonello Laveglia told the press that the Sierre tunnel also meets all Swiss safety norms for ventilation, emergency exits, signalling and energy supply, and that it had undergone a maintenance programme a year ago. Following the devastating loss of life in the Mont Blanc, Tauern and Gotthard tunnels in 1999 and 2001, OFROU checked all Swiss tunnels and presented the results back in 2008. Of the country's 220 highway tunnels, 126 did not meet the newest safety norms. The Sierre tunnel was not one of them. "It met all the safety criteria", said Laveglia.

The 2004 EU Tunnel Safety Directive, which actually only applies to those major tunnels on the trans-European road network, covers all new-build tunnels. In 2014 it becomes retroactive, and EuroTAP has already raised fears that many tunnels (especially in Italy) will struggle to comply with all the regulations once this date arrives.

A EuroTAP inspection of 52 tunnels throughout Europe in 2007 revealed 10 to be either "very poor" or "poor", with a further 12 achieving only an "acceptable" rating.

But the fact is, the minimum safety criteria incorporated within the 2004 Directive do not cover the design of endwalls of safety lanes, merely stipulating at what distances these lanes should be provided at, depending on the overall length of the tunnel and its recorded traffic flow per useable lane. Regulations for unidirectional tunnels are not mentioned at all.

Laybys are covered in Section 2.5 and the requirement is confined to 200 words: "For new bidirectional tunnels of longer than 1,500m where traffic volume is higher than 2,000 vehicles per lane, lay-bys shall be provided at distances which do not exceed 1,000m, if emergency lanes are not provided.

Sierre tunnel entrance portals

"In existing bidirectional tunnels longer than 1,500m with a traffic volume higher than 2,000 vehicles per lane but no emergency lane, the feasibility and effectiveness of the implementation of lay-bys shall be evaluated. If the construction characteristics of the tunnel do not allow it, or allow it only at disproportionate cost, lay-bys do not have to be provided if the total tunnel width which is accessible to vehicles, excluding elevated parts and normal traffic lanes, is at least equal to the width of one normal traffic lane. Lay-bys shall include an emergency station."

There is no data governing the dimensions or the actual construction of the laybys themselves. Interestingly, regulations covering the signage that must be used to indicate the presence of laybys feature an illustration with angled rather than perpendicular endwalls.

It seems clear that while there is no actual legislation or safety directive covering the angle of such endwalls, the fact that the signage demonstrates a human subconscious preference for angled endwalls illustrates that this point is perhaps so obvious as to have escaped everybody's attention, not least tunnel designers.

Emergency lay-by signs illustrate angled end walls

Guido Builman of the Swiss road authority Astra – the organization responsible for Swiss tunnels - told the Swiss press that the Sierre tunnel's safety havens meet all safety requirements. "Depending on the length of the tunnels, there need to be safety havens every 600m to 900m. There are also norms for the corners of the havens. For construction reasons they need to be squared. Until now we did not have any problems with it."

So what could have been done differently? TunnelTalk talked to Dutch tunnel safety expert Evert Sonke, who has more than 17 years experience in tunnel construction and design, with a strong focus on safety. Sonke has managed large Dutch tunnel projects including the Westerschelde tunnel, and Coen tunnels and the current construction of a new traffic tunnel in Maastricht, so is well qualified to offer insights.

He said: "The design choice for a safety haven with perpendicular walls is unfortunate, but I do not think guardrails are the solution here either, they do not offer full protection."

Sonke also points out that guardrails, if applied retrospectively, would limit space in the safety havens.

"A diagonal guardrail at a narrow angle, to protect vehicles from impact with a perpendicular structure and deflect them back on to the main carriageway is not a solution either. I would rather opt for an absorber or crash cushion against the wall."

Crash cushions absorb impacts but take up valuable space

A crash cushion is a steel construction, normally placed at the end of a guardrail, which crumples on impact. It can safely stop passenger cars with collision speeds of up to 100km/h, but the problem here is that crash cushions with strong impact ratings take up a lot of space.

Sonke also points out that Dutch tunnels do not have curbs inside them, which may be important because there is a suggestion that the bus in the Sierre tunnel crash clipped a kerb on the right hand side of the tunnel before going out of control and ploughing into the end wall.

Sonke explained that in The Netherlands "we place a so-called step barrier profile against the tunnel walls which is meant to redirect vehicles scraping against them more gently. This minimises the chance of a vehicle going on to crash frontally into a tunnel wall."

In the aftermath of the tragic tunnel crash in Switzerland, in which it seems that no safety regulations have been breached, what is apparent is that there is a design flaw in having unprotected perpendicular structures inside tunnels. Dedicated emergency lanes running the length of tunnels would be ideal, but short of that, the narrowing of angles of internal walls and providing some form of crash protection or deflective device could be a minimal addition to current regulations.

References

Swiss tunnel crash leaves 28 dead - TunnelTalk, March 2012

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