ACSES

Advanced Civil Speed Enforcement System (ACSES) is a positive train control cab signaling system developed by Alstom. The system is designed to prevent train-to-train collisions, protect against overspeed and protect work crews with temporary speed restrictions. The information about permanent and temporary speed restrictions is transmitted to the train by transponders lying in the track, coded track circuits and digital radio. It is installed on all of Amtrak's Northeast Corridor between Washington and Boston, going fully active in December 2015, a few months after the 2015 Philadelphia train derailment which it would have prevented.

ACSES provides railway trains with positive enforcement of "civil" speed restrictions (those based on the physical characteristics of the line). The on-board components keep track of a train's position and continuously calculates a maximum safe braking curve for upcoming speed restrictions. If the train exceeds the safe braking curve then the brakes are automatically applied.

There are two kinds of speed restrictions which are enforced by the system:

Data regarding permanent speed restrictions and other information about the permanent way and track configuration are loaded into an on-board database while temporary speed restrictions are provided to the train while en route via a wireless data system. The on-board equipment tracks the trains position by counting wheel rotations between a series of fixed Balises set between the rails. In the event a train's crew exceeds a speed restriction a penalty brake application is applied bringing the train to a complete stop in the same fashion as existing automatic train control (ATC) systems.

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