Journal of Accident Investigation

JANA PRICE AND JIM SOUTHWORTH
NATIONWIDE DIFFERENTIAL
GLOBAL POSITIONING SYSTEM
Leonard Allen from the FRA provided an update on the
status of the Nationwide Differential Global Positioning
System (NDGPS), which will facilitate development and
implementation of PTC. Originally developed for the U.S. Coast
Guard near ocean and inland waterways, NDGPS comprises a
series of reference stations throughout the United States that
interact with satellites to provide location information. In
1997, Congress decided to expand the network nationwide,
and it is now operational on single-station coverage over about
92 percent of the land area of the continental U.S. NDGPS
provides 1- to 3-meter position accuracy to receivers capable of
receiving the differential correction signal.
The NDGPS project is now in the process of converting
a group of decommissioned U.S. Air Force ground network
systems to provide additional coverage. Nine Federal agencies
are involved, and the FRA has a lead role as the sponsoring
agency within DOT to increase dual (redundant) coverage from
60 to 100 percent coverage of the continental U.S. According
to the FRA, the NDGPS project has suffered from inadequate
funding. For example, the funding received for the program in
fiscal year 2004 was less than one-quarter of what was requested.
This funding shortfall has led the DOT to reconsider its plan to
pursue development of a high-accuracy NDGPS system, which
would provide accuracy of approximately 10 to 1 centimeters
and could be used to collect data concerning track problems
using instrumented trains.
THE RELATIONSHIP BETWEEN PTC AND
HUMAN PERFORMANCE
Jordan Multer from the Volpe National Transportation
Systems Center opened his presentation by noting that the
number of railroad accidents has gone down, but that the
nature of accidents is changing. Although the proportion of
accidents attributable to mechanical issues has declined, those
attributable to human issues, such as fatigue, distraction, and
medical disability, have increased. PTC creates an additional
layer of defense to systems that are already in place to prevent
human error, such as training and redundant staffing. However,
introduction of PTC technology and features will undoubtedly
add complexity to the system, which may introduce new sources
of errors.
Multer identified a list of human performance factors to
consider when implementing PTC systems. For example, he
noted that some companies claim that when their systems fail,
they revert to their basic non-PTC operational mode, which
would not affect the operation of the system. However, if
human operators are not aware of the system failure, they may
commit errors by behaving as if the system were functional.
Another area of concern Multer identified is interoperability.
For example, when a train leaves one PTC territory and enters
another, how will the in-cab display change? Should there be
one common interface or different interfaces for each railroad?
Multer suggested that involving human operators in the design
process is the best way to address these concerns by fostering
a system design that will accommodate human performance
limitations and allow designers to identify new sources of risk.
These issues have been addressed in multiple FRA research
studies and are highlighted in the new rulemaking.
PANEL DISCUSSIONS
At the end of both days of the symposium, speakers assembled
for a panel discussion with the attendees and throughout the
symposium, audience members were encouraged to submit
questions for the speakers. Multiple issues were raised during
these discussions, including the following:
• Interoperability of various PTC systems
Setting interoperability standards and designing for
interoperability
• Effects of PTC on rail system capacity and efficiency
Locomotive crew feedback on the usability and
effectiveness of PTC systems
• Testing and preparing for software failures
• Protecting systems from tampering or sabotage
Future of investments in railroad train control and
enforcement
• Aging train authority systems
Wayside-centric versus vehicle-centric PTC
architectures
• Track integrity detection systems
•
Energy conservation
CONCLUDING REMARKS
At the end of the symposium, Bob Chipkevich, Director of
the Safety Board’s Office of Railroad, Pipeline, and Hazardous
Materials Investigations, reaffirmed the importance of PTC by
noting that in the last 6 years, the Safety Board has launched
on 38 accidents that could have been prevented by PTC type
systems. Chipkevich concluded,
PTC is a national issue, it’s not a single railroad issue,
it’s not a regional issue. I think it’s important for
78 NTSB JOURNAL OF ACCIDENT INVESTIGATION, SPRING 2006; VOLUME 2, ISSUE 1
•
•
•
•