What is the main operational difference between Automatic Train Stop (ATS) and Automatic Train Control (ATC) systems?

The main operational difference between Automatic Train Stop (ATS) and Automatic Train Control (ATC) systems is that ATS primarily enforces speed restrictions at specific locations and prevents trains from passing signals at danger (red), while ATC provides continuous speed enforcement and can automatically adjust train speed based on track conditions and signal indications. ATS is a simpler system that typically uses wayside signals and trackside equipment to trigger an emergency brake application if a train exceeds the permitted speed at a specific point or attempts to run a red signal. It does not continuously monitor the train's speed or location. In contrast, ATC is a more sophisticated system that continuously monitors the train's speed and location and compares it to the permitted speed profile for the track ahead. The permitted speed profile is determined by factors such as track curvature, gradient, signal indications, and temporary speed restrictions. If the train exceeds the permitted speed, ATC will automatically apply the brakes to reduce the train's speed to the permitted level or stop the train altogether. ATC can also automatically adjust the train's speed based on changing track conditions or signal indications, providing a higher level of safety and efficiency than ATS. For example, if a train is approaching a curve with a reduced speed limit, ATC will automatically slow the train down to the appropriate speed, whereas ATS would only intervene if the train exceeded the speed limit at a specific point just before the curve.