Advanced Civil Speed Enforcement System - General System Design

General System Design

ACSES provides railway trains with positive enforcement of "civil" speed restrictions (those based on the physical characteristics of the line). The on board components keeps 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 train brakes are automatically applied.

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

• Permanent Speed Restrictions are those that represent maximum safe speed for track geometry and other conditions as laid out in the employee timetable.
• Temporary Speed Restrictions apply to all other conditions not covered by the permanent timetable including track defects, lineside hazards and maintenance workers in and around the track area.

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 systems.

Speed restrictions required by the signal system are provided by the legacy Pulse code cab signaling system, which has been in service on various railroads since the 1930s. The cab signal codes are fed into the ACSES cab display unit, which then enforces the more restrictive of the two speeds. The on board ACSES unit is backwards compatible and can function where only the cab signaling is present without the ACSES overlay as well of situations where ACSES is available without cab signals.

ACSES also enforces a positive stop at signals displaying an absolute Stop indication. The on board database allows the train to keep track of when it is approaching an absolute signal and then determine if a positive stop is required depending on cab signal indication and information provided via a local data radio. The system will stop the train in a Positive Stop Zone, extending up to 1000 feet from the absolute stop signal. To pass the stop signal or otherwise move the train in absence of a more favorable signal indication a Stop Release button must be engaged by the engineer before the brakes can be released.

Due to several limitations of the ACSES system and various contingency operations, employees must still be familiar with all permanent and temporary speed restrictions. ACSES is meant to suppliment, not replace employee's knowledge and skills

The combination of continuous cab signals and ACSES meet the definition of a Positive Train Control system by providing collision protection, enforcement of all speed restrictions and enforcement of track possession by maintenance forces. The deployment of ACSES by Amtrak in 2000 created the first wide scale PTC system on the North American rail network.