Freeway Tunnel Safety Research Based On Crash Data And Driving Behavior Analyses

Tunnels play an important role in reducing travel time,protecting ecological environment,and improving operational efficiency and safety of road networks.They have a unique environment for drivers,including semi-enclosed space,frequent changes in luminance level,and monotonous environment.Thus,traffic safety is a more serious concern in the tunnels than on the open-road sections,and also a minor incident in a tunnel may result in severe consequences.Safety impacts of a collision occurring in tunnels on a freeway are even larger due to their higher design speeds,limited safety facilities,and accessibility issues in rescue operations.Consequently,a crash occurring in freeway tunnels affects the safety and efficiency of the tunnel itself and even that of the whole road section.Because of its importance,studies have analyzed the freeway tunnel safety and found that adopting safe driving behavior in a tunnel minimizes the severe outcomes of an incident.Therefore,implementing driveroriented safety policies and conducting public awareness campaigns that emphasize safe driving behavior/habits when driving through freeway tunnels are essential.However,before devising policies and campaigns on the right issues,it is necessary to understand and explore safety-related problems in the tunnels.In this regard,the present research endeavor attempts to investigate the safety of the freeway tunnels from two perspectives.The first is to analyze the freeway tunnel crash data to gain a more objective knowledge of the traffic safety.The second is to explore deep inside driving behaviors using survey questionnaire data to acquire a more subjective understanding of the traffic safety.The key research directions investigated in this dissertation are as follows:First,the dissertation focuses on identifying and exploring the potential risk locations and factors associated with them for the different types(long,medium,and short)of freeway tunnels,which help provide a basis for effective safety countermeasures.In this regard,the entrance and exit parts of a tunnel are mostly considered symmetrical in previous studies,and the different lengths(long,medium,and short)of tunnels have not been separately studied,which can hinder in identifying the risk locations and the associated factors.Therefore,considering the tunnel lighting guidelines,a six-zone approach is proposed,and the data from 156 freeway tunnels in Hunan province,China,are applied for safety analysis.The three types of tunnels with different lengths are analyzed separately for in-depth analysis.The results showed that the most crash-prone zones for long,medium and short tunnels are the mid-zone,entrance,and access zones,respectively.Furthermore,at the tunnel entrance,drivers usually fail to maintain a safe distance,which results in a high proportion of rear-end crashes,while at the tunnel exit,they are prone to do speeding and improper lane change that increases the risk of sideswipe,rollover,and fixture collisions.The crash occurrence mechanism for the different types of freeway tunnels is also discussed.Second,the dissertation reports valuable information regarding the contributory factors to the severity of injuries in freeway tunnel crashes while fully considering the unobserved heterogeneity and its interaction effects.This will help the authorities to develop effective plans and technologies to minimize the severity of crash injuries in these tunnels.For this purpose,a random parameters model with heterogeneity in means and variances was developed based on a comprehensive dataset containing five-year of police-reported tunnel crashes from Hunan province,China.The study observed that apart from other variables considering the unique tunnel driving environment,the summer,young drivers,novice drivers,presence of curves,and different tunnel sections(access,entrance,and outside exit zones)significantly affect the risk of severe injury outcomes.Third,the dissertation attempts to assess the driver’s role in the tunnel traffic safety by exploring their awareness and knowledge gaps,inappropriate habits,and intentions that should be considered while devising effective safety policies and upcoming information campaigns.To achieve the objective,a detailed questionnaire consisting of 52 questions was administered.A total of841 valid responses were collected through on-and off-line surveys only from the drivers who have experienced driving through tunnels.The results showed that there exist several gaps in the drivers’ knowledge regarding tunnel safety and equipment.Drivers often adopt inappropriate habits and behaviors while driving through tunnels.Also,the tunnel environment has a significant influence on the psychological condition of the drivers.Moreover,drivers’ demographic characteristics significantly affect their knowledge,reported habits,behavioral intentions,and psychological condition.Finally,based on the above multiple countermeasures are suggested to improve tunnel traffic safety,such as providing variable message signs to inform drivers about the speeding limits and distance to the tunnel,ensuring periodic maintenance of the illumination in the tunnels according to the lighting guidelines,implementing automatic section speed control for speeding,taking measures to discourage drivers to do lane hopping,educating specific groups of drivers(e.g.,novice and female)about the complex driving environment of the tunnels,conducting information campaigns and tunnel emergency training programs to enhance users’ awareness regarding tunnel safety.