Conventional railroad vehicles, that run on a line with high frequency of sharp curves, have problems such as wheel noise and wear, from insufficient passive steering. To solve this problem, real-time curvature measurement technology must be developed for realizing active steering. In this study, we propose a uniaxial curvature measurement sensor considering applicability to actual railroad vehicles, and analyze its validity in terms of active steering control. Required characteristics of the curvature sensor according to steering control performance, were determined through railroad vehicle dynamics simulations, and actual vehicle driving information. Measurement range of curvature radius is 200 m to 600 m; measurement accuracy is ±3%, and measurement bandwidth is 0.85 Hz. Effectiveness of the developed curvature sensor was analyzed based on behavior of the car body, the bogie and its installation on the vehicle, and curvature of the track was measured in real time on an actual urban railroad vehicle. As a result of the field test, curvature measurement error was obtained within 3%, validating the feasibility of active steering control for the next generation railroad vehicles.