Importance and Applications of Robotic and Autonomous Systems (RAS) in Railway Maintenance Sector: A Review <s> RAS in Tunnel Maintenance <s> Tunnels environments are characterized by dust, humidity, and absence of natural light. Artificial and natural impacts, change in load criteria, or the simple effect of ageing, make tunnels require inspection and maintenance. These operations are commonly performed by human workers taking time and expertise without guarantee quality control. Robotic tunnel inspection and maintenance (RTIM) introduces high productivity, quality and repetitiveness. This paper describes the current trends in the subject, and introduces new technologies such as scenario modeling, robotic platforms, image and ultrasound sensors, control algorithms and decision making strategies. Additionally, the result of several recent and ongoing projects will be presented. <s> BIB001 </s> Importance and Applications of Robotic and Autonomous Systems (RAS) in Railway Maintenance Sector: A Review <s> RAS in Tunnel Maintenance <s> Abstract Nowadays, the vast majority of the tunnel inspection processes are performed manually by qualified operators. The process is subjective and the operators need to face very uncomfortable and even dangerous conditions such as dust environments, absence of light, or toxic substance exposition. Robotic technology can overcome many of these disadvantages and provide quality inspections collecting different types of data. This paper presents the key aspects of tunnel inspection and a survey of the developed robotic tunnel inspection systems up to date. Additionally, two projects regarding automation of the processes involved and future trends will be discussed. <s> BIB002
The majority of railway tunnels are inspected by human technicians and that suffers from human errors, costs, and high inspection time  . Further, atmospheric conditions within tunnels are characterized as dusty, humid, and dark, which acts as hazardous and hostile environments for human workers BIB001 . IRIS Hyrail by Penetradar is a commercially available semi-autonomous tunnel inspection system, which consists of a Ground-penetrating radar (GPR). The inspection module is fixed to a motorized boom, which is mounted on a vehicle that can be driven on the rail tracks. The manufacturer provides specialized software to manage, collect, and display GPR data BIB002 . In addition, Aoshima et al. have proposed an automatic tunnel inner wall deterioration monitoring system. The suggested scheme consists of sensors that are fused to regular train (velocity more than 100 km/h) which is then used capture data on daily basis. The system is capable of scheduling the necessary maintenance upon the detection of any deterioration being discovered by analysing the relationship between the train velocity and the cross-correlation coefficient of the interpolated crack images  .