Evaluation Techniques for Traffic Safety of Operating Highway Tunnels

: With the consideration of frequent occurrence of traffic accidents on operating highway tunnels, the advancement of safety evaluation for highway tunnels in domestic and abroad are systematically summarized. Through the comprehensive analysis of infrastructure factors influencing on traffic safety of highway tunnels, safety checklists focusing on tunnel horizontal and vertical alignment, tunnel portal situation, pavement condition, ventilation and lighting facilities, traffic safety facilities are provided in qualitatively evaluating operating highway tunnels. Based on the concept of risk, risk assessment indices oriented in infrastructure factors, environmental factors and management factors for operation safety of expressway tunnels and standard highway tunnels are put forward. Quantitative evaluation methods based on indices architecture and the corresponding classification criteria for operation safety risk of tunnels are developed.


Preface
In recent years, with the development of national economy and the increasing demand of production and life, the highway transportation in China has developed rapidly, and the construction of highway tunnels has also made great achievements. By 2016, China had built 15,181 road tunnels with a total length of 14,039.7 kilometers, including 815 extra-long tunnels with 3,622.7 kilometers and 3,520 long tunnels with 6,045.5 kilometers. The tunnel belongs to the road section with abrupt change of road environment. The driver needs to deal with a large amount of information in the process of vehicle driving, which is easy to cause operational errors, resulting in the tunnel becoming a section with frequent traffic accidents. As an important means to prevent traffic accidents and reduce the severity of accidents, safety evaluation has been widely used in foreign countries. Therefore, combined with the relevant research results domestic and abroad, through the analysis of the factors affecting the safety of highway tunnel operation, the corresponding safety checklist is prepared, and the quantitative safety assessment methods based on risk assessment are proposed respectively for highway and standard highway tunnels, in order to provide technical support for the safety assessment of highway tunnels in service.

Analysis of research status domestic and abroad
In the world, tunnel safety has always been very concerned. In particular, European countries began to pay attention to the safety of tunnel operation after major fire accidents in Mont Blanc tunnel and Taun tunnel. According to the requirements of "Minimum requirements for tunnel safety in the trans European road network Directive 2004 / 54 / EC of the European Conference / Council of 29 April 2004", it is necessary to carry out safety assessment on the tunnel and set up a special organization eurotest to check and evaluate the risk degree and safety of the existing road tunnel in Europe. Generally speaking, the technology of highway tunnel safety evaluation in European countries has developed earlier and more mature, and the evaluation method is mainly the combination of quantitative and qualitative. But there are also some shortcomings, such as the imperfect evaluation index system, the less consideration of the impact on human behavior and organizational structure, and the weak operability.
The research on the safety evaluation of highway tunnels started late in China. At present, the research mainly focuses on the safety evaluation index system and evaluation methods of tunnel operation or the advanced methods and technologies of the European Union, applying the concepts of risk potential and safety potential. The Specifications for Highway Safety Audit (JTG B05-2015), which was officially implemented in April 2016, only made general regulations on the safety evaluation contents of the existing highway tunnels from the aspects of highway geometry, sight distance, pavement anti-sliding ability, cross section, electromechanical facilities, safety facilities, etc. The existing research results and industry norms are relatively shallow to the special safety evaluation of highway tunnels in service, and lack of detailed evaluation index system and corresponding qualitative and quantitative evaluation methods, which is difficult to meet the safety evaluation requirements of a single tunnel.

Evaluation method based on safety checklist
According to the basic principles of safety engineering, combined with the relevant research results domestic and abroad and the summary and refinement of some typical road tunnel accidents, the safety checklist is a list of problems affecting the traffic safety of tunnels based on the field investigation and observation of some tunnels. When carrying out safety evaluation for highway tunnels in service, according to the safety checklist for issue list, through the review of design documents, field reconnaissance, field test or inquiries related personnel from the tunnel horizontal alignment, vertical alignment, pavement, ventilation, lighting, such as traffic safety facilities for inspection, found the potential risk factors and potential safety hazard. Is the tunnel open normally? Is there emergency lighting? According to site survey and evaluation. Can power supply be ensured in case of partial failure? Is there a continuous power system UPS?
According to site survey and evaluation. Is there an obvious "black and white hole" effect at the tunnel entrance?
According to site survey and evaluation.
Whether the lighting fixtures are clean? According to site survey and evaluation. 7 traffic safety facilities Are tunnel signs, speed limit signs and no overtaking signs set before the tunnel entrance?
According to site survey and evaluation. When the tunnel is long, the traffic volume is large and located in the uphill road section, is lane indication sign set in front of the tunnel entrance?
According to site survey and evaluation.
When the radius of horizontal curve in the tunnel is small, is there a linear guide sign or active luminous contour sign?
According to the design documents and site survey evaluation.
Is the end wall of tunnel portal marked with facade mark? According to site survey and evaluation. Is a zebra crossing in the direction of oblique traffic built in the hard shoulder 50m in front of the tunnel entrance?
According to site survey and evaluation. Is lane change forbidden at the boundary of carriageway 100m in front of the tunnel entrance and 50m behind the tunnel exit?
According to site survey and evaluation. Is the subgrade guardrail gradually transited to the end of the tunnel portal access road?
According to site survey and evaluation. In order to alleviate the "black hole" and "white hole" effects at the entrance and exit of the tunnel, are active light-emitting inducing facilities set up to realize the smooth transition of light and shade level inside and outside the tunnel?
According to site survey and evaluation.
8 fire fighting and rescue facilities Is the number of fire extinguishers in accordance with fire regulations?
According to site survey and evaluation.
Is the fire extinguisher in an open and fixed position and easy to use? According to site survey and evaluation. Is the fire extinguisher dated? Is it regularly inspected and maintained?
According to site survey and evaluation.
Does the fire hose and emergency broadcast system work normally? According to the field test evaluation.
Is the fire hydrant and fire pump adapter in good condition? According to field test evaluation. Is there a fire water reservoir? Is there any accumulation and garbage in the pool?
According to site survey and evaluation.
Is the emergency exit spacing reasonable? Evaluate according to the design documents Is the emergency exit sign set? Is it clearly visible? According to site survey and evaluation. Is the escape way provided with good smoke and fire protection function?
According to site survey and evaluation.
Is there emergency lighting in the escape way? According to site survey and evaluation.

monitoring facilities
Is there a tunnel monitoring center?
According to site survey and evaluation.
Is the tunnel monitoring center manned 24 hours a day? According to on-site inquiry and evaluation.
Is vehicle detector installed? Is the vehicle detector intact? According to site survey and evaluation. Is there a radio broadcast in the whole tunnel? According to site survey and evaluation. Is there an emergency phone? Are emergency telephone signs complete?
According to site survey and evaluation. 10 other facilities Is the long and extra long tunnel provided with a connecting passage at a suitable position outside the tunnel entrance to facilitate vehicle turning around?
According to site survey and evaluation.
For the road section with more heavy vehicles, does the cover strength of drainage side ditch and cable trench in the tunnel meet the requirements of vehicle driving?
Through the evaluation of design documents.
When the tunnel exit is greatly affected by bad weather, such as heavy fog and snowfall, have targeted measures been taken?
According to site survey and evaluation.

Evaluation method based on risk assessment
After many years of operation, some highway tunnels have some problems, such as the aging or defect of fire-fighting equipment, the failure of ventilation and lighting facilities to operate as required, the weak emergency rescue capacity, the inadequate management of dangerous goods transport vehicles, etc., which lead to a large potential safety hazard and traffic accidents. Therefore, in the process of tunnel operation, the concept of risk is introduced, the safety risk of tunnel operation is identified, and its qualitative and quantitative evaluation is carried out, which has attracted the attention of many researchers domestic and abroad, and qualitative and quantitative evaluation methods such as Delphi method, event tree method, checklist method, analytic hierarchy process, fuzzy comprehensive evaluation method are proposed.

4.1.Safety risk assessment of expressway tunnel operation
Because there are many risk factors that affect the safety of highway tunnel operation, some of them, such as driver and vehicle conditions, are difficult to quantify. In order to evaluate the safety risk of expressway tunnel operation accurately, it is necessary to extract the risk factors which are easy to quantitatively or qualitatively evaluate and have great influence on the safety risk of operation on the basis of safety risk identification, and then establish the corresponding risk assessment index system. Combined with the current situation of expressway tunnel operation safety in China and relevant research results domestic and abroad, the tunnel operation safety risk assessment index system as shown in Table 2. It is constructed from three aspects of facility factors, environmental factors and management factors.

Operation safety risk assessment of standard highway tunnel
Since the overtaking tunnel or another tunnel can be used for traffic evacuation and escape in the event of an accident in the expressway tunnel, traffic organization and rescue escape will face greater problems in the event of an accident in the standard highway tunnel, therefore, it is necessary to evaluate the operation safety risk of the standard highway tunnel. Considering that compared with the expressway tunnel, the standard highway tunnel is poor in geometry, ventilation and safety management, on the basis of expressway tunnel operation safety risk evaluation index system, several evaluation indexes are added, and the evaluation index system of standard highway tunnel operation safety risk is proposed as shown in Table 3. The alignment inside and outside the tunnel portal is in poor consistency

50-74
The alignment inside and outside the tunnel portal is in general consistency

25-49
The alignment inside and outside the tunnel portal is in good consistency There is no fire alarm and fire rescue facilities in the tunnel or the facilities cannot be used normally 75-100

R18
γ18 T18=γ18×R 18 There are only a few fire alarm and fire rescue facilities in the tunnel or some facilities cannot be used normally

50-74
Some fire alarm and fire rescue facilities in the tunnel cannot be used normally

25-49
Necessary fire alarm and rescue facilities shall be set in the tunnel 0-24

Monitoring facilitiesT19
There is no monitoring facility in the tunnel or the monitoring facility cannot be used normally The emergency rescue capability is relatively poor 50-74 For traffic accidents, fire has a certain rescue ability 25-49 There is a complete rescue force and a complete emergency plan 0-24 According to the risk assessment index system established in Table 2 and Table 3, the safety risk of tunnel operation is evaluated by the index system method. The safety risk of tunnel operation shall be determined according to formula (1) and (2).
Where: n -number of evaluation index items; mimportance sequence number. m ≤ n .
Through expert consultation and discussion, the importance ranking of safety risk assessment indicators for expressway and standard highway tunnel operation is determined, and the weight coefficient of safety risk assessment indicators for expressway tunnel operation is calculated by formula (3) as shown in Table 4. The weight coefficient of the risk assessment index of the operation safety of the standard highway tunnel can also be determined according to the similar process.
After the calculated value, the safety risk level of tunnel operation is determined according to Table 5.

Conclusion
With the rapid development of highway tunnel construction in China, the safety situation of highway tunnel operation is not optimistic, so it is very urgent to evaluate the safety of highway tunnel in service. Combined with the research status of safety evaluation of highway tunnels domestic and abroad, the safety checklist of highway tunnels is compiled by summarizing and analyzing the facility factors that affect the traffic safety of highway tunnels in China. Based on the concept of risk, the evaluation index system of tunnel operation safety risk is formed from three aspects: facility factor, environment factor and management factor. The evaluation index system of operation safety risk and the quantitative evaluation method of tunnel operation safety based on the index system method are proposed for the expressway and standard highway respectively, which is used to carry out the special safety evaluation of highway tunnel in service and provide technical support for the daily management and maintenance work and safety self inspection of the tunnel operation management unit.