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Automatically
ensuring stops and speed restrictions, Positive Train Control (PTC) acts as an
‘air traffic control’ for ground transportation. “At any one time, there are
tens of thousands of freight and passenger trains in operation in the U.S.,
sharing nearly 25,000 miles of rail line.
Congress has
tasked the industry with advancing the safety of rail travel beyond the
conceptual premise. The Rail Safety Improvement Act of 2008 required PTC
implementation by the end of 2015. The mandate is intended to:
- Prevent train-to-train collisions
- Enforce speed restrictions
- Prevent movements over a switch in the wrong position
- Protect roadway workers and their equipment
PTC utilizes
onboard and wayside systems as well as back office servers tied together by a
wireless communications system. With PTC, trains receive information from GPS and/or
transponders about their locations and where they are allowed to travel safely.
The systems, also known as movement authorities, determine when braking should
start so that a signal is not overrun and if the braking operator does not act
for any reason, will enforce braking. Speed and authority limits are monitored
by the train’s speed curve and a distance-to-target or breaking curve formula.
PTC is activated when the train is no longer operating at allowed speeds or is
braking insufficiently to stop short of the end authority.
The United States
is currently deploying two PTC Systems, The Electronic Train Management System
(ETMS) and the Advanced Civil Speed Enforcement System (ACSES). The ETMS which
is used by most Class 1 freight carriers is applicable to medium-density train
tracks with speeds of 70 mph or less. The ACSES is a safety critical system
that overlays an existing cab signal system.
It is not a case
of “off the shelf” availability although most of PTC system electronic
components already exist. In order to support interoperability, a common means
of wireless data communications needs to be established. Led by the Class 1
freight railroads, the use of 220 MHz radio channel is being adopted. Without
FCC allocation, each railroad has been left to acquire channel and licensure
covering their operation areas. Host railroads must document in their
implementation plans including how they are interoperable with their tenant
railroads or vice versa. Support for interoperability must be proved for the
PTC system to be certified by the FRA.
With most
commuter railroads operating at a deficit, costs inevitably fall to the
taxpayer. With an average of $130,000US per mile, it is likely that scheduled railroad
maintenance will be deferred to meet the 2015 Congressional deadline for PTC
implementation. Railroads continue to seek a business benefit to PTC technology
including:
- Improved real time diagnostics of locomotive and signal
equipment
- Improved management of train operations through more precise
location
- Improved capacity
There is the need
to demonstrate the extension of PTC technologies to combined heavy freight
density and passenger service corridors. The newer PTC systems designed for
application to major freight lines have neither been implemented nor tested
under mixed traffic conditions. Given the vulnerability of passenger trains
with respect to freight trains in a collision scenario, such testing is
necessary to ensure that the PTC functions will operate correctly. Only time
will tell if the Rail Industry’s progress towards the Rail Safety Improvement
Act proves successful.
Sources:
http://www.fra.dot.gov/rrs/pages/fp_1265.shtml
http://www.fra.dot.gov/pages/784.shtml
http://www.fra.dot.gov/pages/1804.shtml
http://www.fra.dot.gov/pages/947.shtml
http://www.metro-magazine.com
http://www.lockheedmartin.com
http://www.protectiongroup.com/
http://www.wsdot.wa.gov/
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