Analysis of Important Factors Having an Impact on Safety in Road Tunnels – Research Findings

Aim: This article presents relevant safety issues in road tunnels based on the results of a survey and evacuation experiments conducted on real scale in two existing road tunnels in Poland. Project and methods: An analysis of the relevant factors influencing the level of safety in road tunnels was carried out based on the results of experi mental studies in two road tunnels in which the course of evacuation under fire conditions was observed. As part of the study, several evacuation trials were carried out at equal smoke levels, examining a different parameter each time: pre-movement time, speed of movement, the effect of smoke on the speed of movement, the effect of tunnel infrastructure on evacuation, among others. A survey carried out among 504 respondents, in turn, attempted to assess the awareness of hazards and safety procedures in road tunnels. The survey has four parts and questions covered the following issues: knowl edge of tunnel infrastructure, behaviour in case of congestion, choice of evacuation route, behaviour during the evacuation, personal belongings during the evacuation, self-assessment of tunnel safety knowledge and the role of experience. An analysis was also carried out of the information available in Poland on safety guidelines for road tunnels, which can help tunnel users to improve their knowledge on tunnel safety. Results: The survey results indicate an insufficient level of knowledge regarding safety in road tunnels – only 16% of respondents answered more than 50% of the questions correctly. Ignorance of road tunnel infrastructure itself and the safety rules for the tunnel was also diagnosed. An analysis of the information available to the road users demonstrates that this information is difficult to access and that there is a lack of uniform guidelines to educate the public on the topic raised in the article. A significant impact of evacuation exercises carried out on an accurate scale was emphasised, providing valuable data on the evacuation process and increasing the level of safety in the engineering facilities analysed by raising the awareness of the partici pants in the experiment. Conclusions: The research findings presented in this article allow for better understanding of the behaviour of the participants of accidents and fires in road tunnels. In addition, the need to raise the awareness of the road users on the dangerous situations that may occur in a tunnel and the appropriate response to them has been demonstrated.


Introduction
Road tunnels are more and more often an essential part of road infrastructure, so the safety aspect of these structures has become a frequent subject of research by scientists. Although from a statistical point of view, the accident rate in tunnels is lower than for open roads, it is worth noting that due to the geometrical characteristics of road tunnels the effects of hazardous situations may be on a different scale compared to open road spaces [1]. It should be emphasised that the consequences of accidents in partially enclosed spaces, such as tunnels, can be much more severe [2]. The above is evidenced by the tragic consequences of tunnel fires, e.g. in the Mont Blanc tunnel in 1999, where 39 people died, mainly because these people failed to evacuate, probably due to unawareness of the danger and ignorance of safety procedures [3]. Pomimo że ze statystycznego punktu widzenia, wskaźnik wypadkowości w tunelach jest niższy niż w przypadku dróg otwartych, to warto zauważyć, że ze względu na charakterystykę geometryczną tuneli drogowych skutki sytuacji niebezpiecznych mogą mieć inną skalę w porównaniu do otwartych przestrzeni drogowych [1]. Należy podkreślić, że konsekwencje wypadków w częściowo zamkniętych przestrzeniach, takich jak tunele, mogą być znacznie poważniejsze [2]. Świadczą o tym tragiczne konsekwencje pożarów w tunelach, np. w tunelu Mont Blanc w 1999 r., gdzie zginęło 39 osób, głównie dlatego, że osoby te nie podjęły ewakuacji -prawdopodobnie z powodu nieświadomości zagrożenia i nieznajomości procedur bezpieczeństwa [3]. Podobny scenariusz miał miejsce podczas poża- This article presents essential aspects related to safety in a road tunnel taking into account the results of fire evacuation tests conducted on a real scale. The aim of the publication is to show the role of the human factor, in particular the lack of knowledge of potential drivers about safety affecting the level of safety in tunnels. Recent studies proved that an essential factor affecting accident rates is the level of knowledge of the road users, not only drivers but also passengers [4]. Therefore, this article also includes the results of own research on the preliminary diagnosis of the assessment of awareness and knowledge of the safe operation of tunnel infrastructure among potential users of road tunnels.

Potentially dangerous situations in a road tunnel
During the operation of traffic tunnels, a user is exposed to many hazards, including increased concentration levels of harmful solid and gaseous pollutants, vehicle collisions, leakage of toxic substances, etc. From the point of view of the hazard scale, fires are the most significant and most dangerous incidents in tunnels. According to the statistics, they do not occur very often, but their effects in a semi-enclosed space such as a tunnel can be much more severe compared to open traffic routes. Unlike open fires, a fire in a space enclosed on four sides, such as a road tunnel, can be characterised by rapid development. There is also a likelihood of a fire spreading to other vehicles, causing an increase in firepower, as happened in 2001 in the St. Gotthard tunnel [14]. 86 fatalities, 68 injured, 100 vehicles damaged were the consequence of just four fires in road tunnels: Mont Blanc, St. Gotthard, Tauren, Wuxi Lihu, which gives a picture of the danger of such incidents and a much higher risk than for traffic accidents in open spaces [5].
A fire in a tunnel can last for several days and cause enormous losses not only in material assets, the tunnel construction (see Figure 1.) but also in the surrounding area, significantly reducing its communication and tourist value, as happened after the fire in the Mont Blanc tunnel in 1999. It took more than 50 hours to extinguish the fire completely, and the tunnel was only reopened after three years. However, the tragic consequences of this disaster in the form of 39 fatalities are undoubtedly the most significant loss [3].

Assessment of tunnel safety awareness and knowledge
An attempt to assess the awareness of safety procedures was made on a group of 504 respondents by conducting a survey among them, detailed results are presented in the article [6].
The questionnaire has four parts. The first dealt with the identifi- On average, the respondents answered 5 out of 15 questions correctly. Only 16% of the respondents answered more than 50% of the questions correctly. Moreover, no one indicated correct answers to 12 or more questions. Interestingly, most respondents were confident that they had better knowledge of road tunnel safety than they actually did.
The results indicate the need for educational activities among the public so that safety levels increase and the complex safety systems operating in road tunnels support the conscious actions of its users [6].
Based on the results of the survey, the following findings
The results of part 3 of the survey, which dealt with safety rules, indicated that the respondents greatly overestimated their knowledge, as 88% of them did not answer even half of the questions correctly. Comparing the above with the respondents' statements, it is reasonable to conclude that the respondents overestimated their knowledge and lacked it [6].

Where can I find information on safety rules in a road tunnel?
Let us imagine that we are travelling by car in Poland. We set instructions may not only be different in their scope (as the parameters of the tunnels are different), but they may be located in different places. In the age of the Internet, it is not a significant problem to access this knowledge, but with the multitude of things to be done and the fast pace of life, there is probably not enough time for it.

The role of research in improving safety in road tunnels
As a consequence of the fires in tunnels that have occurred in the last several years, measures have been taken to improve safety during tunnel operation, as evidenced by the legislation issued, among others [7][8], and numerous scientific studies concerning for instance evacuation behaviour [6,9], movement speed [10], tunnel infrastructure [11], evacuation exit [12] or  In the last two trials, where the smoke was the strongest, evacuees observed disorientation due to significantly reduced visibility (see Figure 3). Synchronised cameras were used to measure the times of the various evacuation stages, and thermal imaging was used to track the behaviour of users in smoke-filled areas. It should be emphasized that during a real fire, smoke and fire gases are very toxic and pose a lethal threat to the evacuees.    The flow of evacuees, as well as observations of the participants' behaviour, were carried out using a set of cameras. In addition, thermal imaging cameras were used due to very poor visibility in the vicinity of the coach. To precisely measure the evacuation time of each unit, the organisers used ChronoTrack measurement technology based on UHF technology.
During the first of the three trials of the experiment, the participants were provided with no information about the conduct of the study, the rules of behaviour, the presence of smoke, and the tunnel's infrastructure. The signal to start evacuation was the occurrence of a situation analogous to an actual fire incident: smoke appeared in the tunnel (see Figure 4), and the fire procedure was activated (including fire lighting, voice announcements and alarm signal). In the last trial, where 40 out of 90 participants were given the task of simulating illness, injury or death, the time taken for the Fire Service to arrive at the scene and the process of segregating the injured were examined (see Figure 5).
Both experiments were conducted using non-toxic, cold smoke so that the conditions during the tests mirrored those during a fire as closely as possible. In addition, to ensure the safety of the participants, the experiment was conducted with the participation of the Fire Brigade, the Police and the medical services. Naturally, the tunnels were closed to vehicle traffic for the duration of the study. A detailed course of the evacuation experiment in the Emilia tunnel in Laliki, together with the research results, is included in the scientific study [6].

Summary
This material highlights the level of safety knowledge and hazard awareness in road tunnels among a large group of the respondents [6]. Based on the results of the survey, it can be concluded that there is a need to increase the level of safety in tunnels, not only through the use of various modern systems in these facilities but also by raising public awareness of the tunnel infrastructure itself, the situations that can happen in it and the appropriate response to them. Taking into account the availability of existing information in this field, it would be advisable to develop a comprehensive general education programme with a broad "impact" range, without dedication to a specific facility, the use of all tunnels in its scope. Regardless of the country, the length of the tunnel or its design parameters, a potential road tunnel user should be able to respond correctly to a specific incident.
It is also important to emphasise that the real-scale evacuation drills have a huge impact on increasing the level of safety in the analysed engineering facilities [9,[11][12]. People with such experience acquire the ability to appropriately react to potentially dangerous situations, are familiar with the infrastructure of the tunnel, which significantly speeds up the evacuation process by eliminating the delay in the start of the evacuation, so often observed during fires in tunnels (reaction time and decision to evacuate) [9,[13][14], very often excluding the chance to safely leave the endangered place (the most frequent cause of the loss of life).
It should be emphasized the importance of such research, the results of which can be widely used, e.g. for educational purposes, when designing the tunnel infrastructure, as well as during numerical modeling studies, where appropriately selected initial-boundary parameters resulting from real experiments allow a better reflection of reality by the numerical model.
Awareness, knowledge and skillful reaction to potentially dangerous situations among drivers will result in a high level of safety in road tunnels, as it is well known that prevention is much more effective (not only economically) than treating the consequences, often very tragic ones.