The use of smart sensors has been a game changer in modern railway business. Through digitalization, railway performances become measurable and observable in ways never seen before. Human factors during train operation can also be quantified and improved, minimizing the number of unwanted incidents and injuries due to human error. An automatic and standalone device has been developed by MTR engineers to alert train captains during train shunting. The design employs a high caliber microprocessor, an integrated RADAR sensing module, a SD card module for data recording, and self-implemented data filtering software for smooth detection and quick response. The solution is also highly agile in various environment, including tunnel, outdoor and depot areas. Compared with the conventional shunting operation that solely depends on manual operation, ARSDA further allows the data analysis of train captains’ performances using records of each shunting operation. By plotting the data against a safe driving profile, the operation performances can be evaluated based on the recorded approaching speed and acceleration. With multiple tests already conducted, these data are currently in trial as a part of training for train captains, as safety is always the ultimate goal of daily operation in MTR.