Michael J. Ehrenberger

Railroad & Transit Project Manager

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Dec 15, 2020

Over the past two decades, positive train control (PTC) technology has evolved from one of the National Transportation Safety Board’s “most-wanted” safety initiatives to standardized operating procedure along the busiest train routes in the country.

This month provides two opportunities to acknowledge this engineering success story. Both milestones are cause for celebration.

December marks the 20th anniversary of the introduction of ACSES PTC into revenue service on the Northeast Corridor aboard the first regularly scheduled run of Amtrak’s Acela Express. The end of the year also brings success in reaching the PTC deadline for full implementation on the Northeast Corridor (NEC).

Federal law requires PTC installation by December 31 on Class I commuter rail lines or any railroads that transport hazardous materials. All 41 commuter railroads subject to the mandate are expected to meet the 2020 deadline.

“Widespread use of PTC systems is likely to prevent collisions and save lives.”

Widespread use of PTC systems is likely to prevent collisions and save lives. PTC systems reliably and functionally prevent train-to-train collisions, overspeed derailments, incursion into established work zones, and movement through a mainline switch in the improper position, among other functions.

To mark this accomplishment, I reflected on the evolution of some of the technology that makes PTC possible at the American Railway Engineering and Maintenance-of-Way Association 2020 Virtual Conference. AREMA members can view my presentation and read the full paper.

The Advanced Civil Speed Enforcement System (ACSES) is a transponder-based system that has become the predominant PTC system throughout the Northeast Corridor.

“ACSES PTC is built on layers of tried and true technology. ”


ACSES PTC is built on layers of tried and true technology. At its foundation is the wayside signal system and Automatic Train Control (ATC) Cab signal, providing signal speed enforcement, safe train separation, and protection from broken rail. ACSES provides a vital overlay for the enforcement of permanent civil speed limits and temporary speed restrictions. ACSES and ATC Cab signal interact to enforce positive train stops. Together, ACSES and ATC Cab signal provide full PTC functionality.

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“As train technology advances, PTC systems will continue to be enhanced and refined.”


Among the greatest accomplishments in my career has been the development of ACSES technology. In December 1998, I joined colleagues at Alstom, Amtrak and PHW, Inc (now Siemens Mobility) to conduct the initial ACSES field tests.

Much has changed since those days on the snow-covered desert plains at the Association of American Railroads’ Transportation Center, Inc., in Pueblo, CO. ACSES PTC systems are now in revenue service demonstration or in operation across all railroads operating on the NEC and feeder lines.

ACSES technology continues to evolve, working toward new functionality and seamless interoperability. The next generation will incorporate an onboard database to “fill in” missing information if a full transponder set is not read successfully.

Also on the horizon, Amtrak’s new highspeed trainset – Avelia Liberty – is targeted for revenue service operation next year at speeds up to 160 MPH. As train technology advances, PTC systems will continue to be enhanced and refined.


Although this may have been a historic year with heartbreaking challenges, let’s close out 2020 on a positive note, acknowledging the success of PTC technology. With its implementation, commuters and railway operators are now safer and more prepared for whatever challenges the future will bring. We’re all aboard for another 20 years of safe travel and technological advances.