# Performance Evaluation of Track Curvature Sensor for
## 1 Introduction  
A railway track is composed of a straight track and a curved track of various curvature radii. When a railway vehicle runs at high speed on a straight track, running stability according to high speed is required. On the other hand, when railway vehicles run on a curved track, the force applied by the wheels to the rail is increased because of centrifugal force, which restricts the speed at which the vehicles pass through curves and occasionally causes problems such as severe wear and noise of the wheel and rail [1, 2]. The speed limitation on the curved section adversely affects the commercial operation of the railway, and severe wear of the wheels and rails results in early replacement of the wheels and rails, which increases the cost of vehicle maintenance. In addition, dust and noise caused by wear deteriorate the air quality of the railway section, adversely affecting the comfort of railway users. Hence, active railway vehicle technology has been developed to resolve the above-mentioned problems. As a means to solve the speed limitation on the curved section, a tilting train has been developed to increase the speed of the curve by tilting the car body of the vehicle inward of the curve to reduce centrifugal force [3]. In addition, research on active steering technology has been conducted to reduce the wear and noise of wheels and rails running on curved sections [4, 5, 6]. At this time, the core technology needed is curve detection technology to detect the curved track. Tilting technology or active steering technology to improve curve running performance should be activated only in the curved section, so it is necessary to accurately detect curves and detect curve information such as curve radius and curvature. In this regard, the following curve detection technology has been developed. As the oldest method, a curve detection method was used, in which the position and curvature of the curve were input in advance to the lookup table and used in the form of a lookup table [7]. To apply this method for vehicle control, it is only possible to use it by accurately detecting the beginning and end of the curve and the position of the curve. If the operating track is changed, curve information for a changed track must be input into the lookup table again and utilized, and if the position is detected incorrectly while the vehicle is running, it may adversely affect vehicle safety and control. There is an internal measurement system using gyro sensors, acceleration sensors and speed sensors, which enables real-time measurement while a vehicle is running. This method has a disadvantage in that an offset error occurs due to the integration process in the curve extraction algorithm and is affected by the vehicle's running speed [8; 9; 10]. In addition, the above methods are inefficient because test processes are required to correct errors in curve detection through many test runs in advance. Another method to detect curves is the code measurement system. This method is mainly applied to track inspection cars that measure the state of the track for track maintenance. The principle of measuring three points of a curve at regular intervals to extract curvature from a geometric relationship is used. It is applied only to track inspection cars for track maintenance by measuring three points of a curve in a non-contact type, while running using an expensive optical sensor [11]. In addition, many studies have been conducted on the suitability of vehicle dynamics and railway transition curves from the perspective of railway infrastructure design [12; 13]. Since the existing curvature detection method as described above has disadvantages and inefficiencies, a new curve detection technology for efficiently controlling a vehicle in a curve section in real time is required. From this background, the author proposed a new curve detection method to extract curvature using the geometric relationship between the vehicle and the track in the curved section [14].