Search underway for tunnel accident causes

June 19, 2011: a bus accident at the entry to a tunnel on the Zurich bypass Keystone

An increase in accidents at the Gubrist tunnel, Switzerland’s busiest, has led researchers to develop a simulator in an effort to discover the cause.

Switzerland is a country of tunnels, with more than 220 – the equivalent of about 11 to 12 per cent of the 1,800 kilometres of national roads. And there have been many fatal accidents.

In March 1999, a fire in the Mont Blanc tunnel caused the deaths of 39 people, while in May of the same year, 12 people lost their lives in a fire in Austria’s Tauern tunnel.

A further 11 people were killed in an accident in the Gotthard tunnel in October 2001.

The inherent dangers of driving in tunnels are well known and European countries are conscious of the need to regularly inspect and renovate tunnels when needed.

While major accidents cause headline news, another danger less spoken about is the entrances and exits of tunnels where numerous accidents occur.

Now, researchers at the Federal Institute of Technology in Zurich (ETHZ) have teamed up with the Federal Roads Office in an effort to discover why so many accidents occur at these hot spots.

Accident hot spots

“We don’t have detailed statistics,” said federal office spokesman Thomas Rohrbach. “It is clear that there are fewer accidents than on open roads. Nevertheless, we have noticed, in recent years, an increase in accidents in the Gubrist tunnel, on the northern bypass of Zurich, which is the busiest tunnel in Switzerland.”

“This tunnel alone is responsible for a third of traffic jams on the national roads. A jam here has repercussions for other sections. A minor accident is enough. That’s why we want to know the causes of these accidents.”

At the request of the Roads Office, vision specialist Professor Marino Menozzi and his team at the ETHZ have begun a three year study to find the reason for the increase in accidents and to propose possible solutions. The study is being co-financed by canton Zurich.

According to Menozzi, statistics show that the most sensitive zones in tunnels are relatively small.

“From the information provided by canton Zurich, we found a large increase in the frequency of accidents in the first 200 metres after the entry of the tunnel,” said Menozzi.

The number of accidents then declines inside the tunnel, but again increases around 200 to 400 metres before the exit of the tunnel, he said.

Eyes and light

In his laboratory – an old garage measuring about 20 square metres equipped with a simulator made of a car seat, steering wheel, and three pedals connected to a bank of computers – Menozzi plans to study the effects of light contrast on the eye when entering and exiting tunnels.

“Studies have already been done on the luminescence between around 8,000 candelas (the unit used to measure the brightness of a light source seen by the human eye) by square metre outside and 50-60 candelas by metre squared inside, just after the entry,” said Menozzi.

“The eye needs a moment to adapt. For an instant, the driver is blinded. The perception of movement is affected and that can produce a momentary lack of attention.”

The effects of a bigger contrast have not yet been studied. At the entry to the new Uetliberg tunnel on the western Zurich bypass, Menozzi measured 14,000 candelas per square metre outside.

Aging population

Menozzi says the problem of contrast threatens to become more acute with the aging of the population. A 55-year-old person needs more light and is more sensitive to glare than a person who is aged 20, he says.

But light contrast is not the only obstacle at the beginning of the tunnel: the architecture, colour and choice of building materials also play a role.

“Concrete is becoming more and more pale in colour and reflects more light,” said Menozzi. “The use of dark green around the entrancies in the past was better at reducing glare.”

The simulator enables Menozzi and his team to carry out tests – the number of which must be determined to obtain representative results – in different light contrasts. The researchers want to measure drivers’ perception of speed, the position of the vehicle in front and how they understand signs or other objects in the environment around the entrancies and exits to tunnels.

The pupil of the eye will be analysed with the test subject wearing a sort of helmet connected to the computer that then registers the movement of the eye.

“We want to know where the driver looks when he enters the tunnel,” said Menozzi.

Other experiences

One option might be to increase the light at the beginning of the tunnel, for example for the first 50 metres, in an effort to reduce the contrast.

“That would present a problem of energy consumption,” said Menozzi. “The western Zurich bypass already consumes as much energy as a small village… On the other hand, the cost of a minor car accident is SFr40,000 ($47,700), which is also a lot of money.”

Menozzi doesn’t want to stop at the tunnels. Pre-tests are already available on the simulator to analyse the peripheral vision of drivers.

“From this, we could determine how much information the driver can register. We are also going to test different types of routes, for example next to construction sites. Is there too much information or not enough?”

Menozzi does not think it will be necessary to drastically alter tunnel entrances and exits.

“The roofs installed at the entry of certain tunnels to create a transition zone seem to work quite well. And they are certainly more acceptable than speed limits or insisting on a five minute stop in the shade to adjust to the darkness,” said Menozzi.

Tunnels

Europe has about 700 road tunnels longer than one kilometre and including eight tunnels which are longer than ten kilometres.

Zurich. The Gubrist tunnel (3.3 km), on the northern Zurich bypass has seen an increase in the number of accidents occurring at its entries and exits. According to cantonal police, there have been 88 accidents here in the past five years.

Gotthard. In canton Uri, where the northern entrance to the Gotthard tunnel is located, police report accidents near the entrance are less frequent than on the open roads. “Measures have been taken to ensure that heavy vehicles enter the tunnel in a regulated manner so that traffic flow in the tunnel is uniform,” police said.

Since the introduction of these measures in the wake of the accident in 2001, the number of accidents in the tunnel has significantly declined, according to police.

Standards. All tunnels respect international standards which dictate that a certain percentage of outside light must be guaranteed at the entry to the tunnel.

(Translated from French by Sophie Douez)