| Advanced Communications In Transportation |
| Telecommunications Control of Transit Station
Fare Gates |
| By James Schmid, Atlanta, Georgia, 1-404-870-3253,
c/o mjohnson@ogc.itsmarta.com |
| A low-tech, cost-effective solution met the challenge
of transferring several unique systems to one central control point
when MARTA transferred the functions of its six zones to one operations
center. |
|
|
This section illustrates the range of communications
work that PB does within the transportation sector. It starts
with five articles written by staff members on Metropolitan
Atlanta Rapid Transit Authority (MARTA) projects. PB gained
much of its early telecommunications experience working on
MARTA, the company’s longest-term project. Our more
current MARTA work involves cutting edge technology involving
voice, data and video networks and communications, and the
infrastructure that makes it all possible.
MARTA provides rail, bus and
para-transit service to Atlanta, Georgia and two contiguous
counties, including the area’s regional airport. It
consists of a 73.1 km (45.4-mile) multitrack rail system with
36 passenger stations, two rail yards and plans for another,
three bus garages and several support facilities. PB has been
involved in MARTA projects for more than 30 years as a senior
member of the general engineering consultant joint venture
to MARTA known as Parsons Brinckerhoff Tudor – Turner
Associates (PBT-TA). Our support began with conceptual design
and has continued through installation, operation, several
expansions and some renovations.
|
MARTA’s rail service is divided into six zones, each of which
had, until recently, a center where police, patron assistance and
elevator phones were routed to zone center operators. Other functions
of the zone centers included the monitoring of station security cameras
and control of station fare gates and public address systems.
MARTA recently completed a project whereby the zone centers were closed
and many of their functions were moved to one central operations center,
which came to be called the Police Operations Center (POC). This project
required redirecting the fare gate control from six different locations
to one location serving 36 stations.
The Problem
The MARTA rail station fare gates had always been controlled by zone
center operators who could open one gate at each entrance to the different
stations within the zone and who could also issue bus transfers. The
fare gates would perform these two actions upon sensing a short circuit
signal of a specified duration on two of its input leads. A short
of one duration would open the fare gate and a short of a longer duration
would cause the gate to issue a transfer.
The operators controlled these actions by utilizing auxiliary outputs
from the closed circuit television (CCTV) system controllers at each
station. After an operator had pressed a button on his or her console
to either open a gate or issue a bus transfer, one of the CCTV controllers
at the appropriate station would sense the request and issue the proper
command to the fare gates. (The CCTV controllers control the fare
gates and the cameras.) Because the rail stations were built over
a period of approximately 20 years, however, the CCTV systems at each
station differed in their technology and implementation of these commands.
Therefore, transferring this control that was being carried out by
several unique systems to one central control point was a challenge.
Investigation and Resolution
The various CCTV controllers in each zone use proprietary protocols
to control the CCTV cameras (pan, tilt, zoom) and the auxiliary outputs,
which included controlling the fare gates. We investigated three options
for transferring control of the fare gates to a single location.
Option 1: Replacing CCTV Controllers. More than 50
percent of the CCTV controllers would have had to be replaced or substantially
modified to provide control of the fare gates from a single point
using the CCTV system. This option was not used because it proved
to be less cost-effective than Option 3.
Option 2: Programmable Logic Controllers. Deploying
a programmable logic controller (PLC) at each station would provide
a short upon receiving a command from the POC. This option would require:
- Development and procurement of the application
specific PLCs
- Provision of power to each PLC
- Installation of wiring to each station to provide communications
to the PLCs from the POC.
This option proved to be relatively costly due to the development
of the PLCs and the installation of additional circuits that would
be required.
MARTA Central Control Atlanta, Georgia |
Option 3. Dual-Tone Multi-frequency Decoders. The
third option, which was implemented, utilized off-the-shelf dual-tone
multi-frequency (DTMF) decoders to control the gates. A DTMF decoder
can be programmed to provide a short for a specified duration upon
receiving a certain DTMF code over, for example, a phone line.
Requests for entrance through the fare gates or issuance of a transfer
typically come from patrons whose fare card is not being read or who
have lost their ride token in the fare gates. These patrons call the
POC on the patron assist phones located at each station for either
entry through the gate or a bus transfer. At this point, the operator
at the POC is on the phone line to that station. When the operator
enters the proper code through the telephone keypad, the DTMF decoder’s
relays are energized to exercise the requested fare gate operation
(pass through or transfer issuance).
The input of the DTMF decoder is spliced to the existing patron assist
phone circuit. The outputs of the DTMF decoders were spliced directly
into the input control lines of the fare gates. The DTMF decoders
used 120-vac power, which was readily available in all of the train
control rooms.
Conclusion
The installation of the DTMF decoders proved to be the most cost-effective
solution to relocating the control of the fare gates from six different
centers using different control protocols to one central location.
The DTMF decoders are small, simple boxes with numerous outputs so
that two could typically control all the fare gates at a station.
Because control of the DTMF decoders occurs via the phone lines, no
new circuits had to be installed.
This project showed that using off-the-shelf technology and existing
resources proved to be a more cost-effective approach to solving certain
problems than developing a new application- specific device. |
|
| Jim Schmid is a communications engineer
who has been with PBT-TA in Atlanta, Georgia for approximately two
years. He has worked in the cellular industry for several years and
as an avionics integration engineer in the aerospace industry with
a specialty in communications systems. Jim was part of the team that
provided cellular communications for the 1996 Olympics. |
|
