|
Altogether we look after about 755 signals in the Durban and
surrounding area and most of them are connected back to one of 2 systems
to monitors faults. Where possible we try to provide a direct cable link
from each controller to the Control Centre and these signals are
connected to what is known as the Area Traffic Control System. This
system is run on a powerful computer which interrogates the controllers
every second through this transmission unit. The instation computer can
now control the traffic signals and check for faults such as lamps out,
power failure / signal out, poor communications, broken detectors /
pushbuttons etc. If necessary the operator can easily intervene from the
instation to vary the timings or implement new timings directly. Apart
from the signal control and fault monitoring the ATC sustem provides
facilities such as:
- lamp dimming to reduce glare from signals at night & save
electricity
- emergency routing - transponders fitted to give priority to police
for eg.
- green wave on routes for evacuation / fire engines
- traffic responsive control - adv. of VA but with
synchronisation
There are approx. 400 signals on this system, including those in the
nearby town of Pinetown.
This Branch, assisted by consultants, has developed the
Sentinel ATC System which is essentially a user friendly front-end
to the Area Traffic Control System and also allows the flexibility of
connecting other types of controllers to the system if required at some
later date.
In the outlying areas where it is too expensive to run dedicated
cables from the Traffic Control Centre signals are connected to a Remote
Monitoring system. Here the controller actually reports faults by phone,
using the normal TELKOM lines using a slightly different comms. unit.
This system monitors all the usual faults but only offers limited
control from the PC based instation. There will eventually be about 70
controllers on this system.
A combination of reliability problems and increasing operating costs
(both transmission units and telephone line rental) necessitated the
in-house development of a
telemetry fault reporting system which is currently still being
tested.
Getting back to the actual signal controller, it can of course
operate independently on the signal timings stored in its memory. Even
if the signal is under Area Traffic Control there will be occasions when
communications break down (cable cut), in which case the controller
checks the time of day and implements its timings for that period. A
quartz clock is used, which is very accurate, and this insures that if
the signals are synchronised they will continue to run in the same
manner relative to each other and the motorist won't know any different.
This facility is known as cableless linking so that signals can be
synchronised without a physical cable link between them. Another useful
facility is the police pannel which allows one to override the
controller operation on site - like doing point duty from the
pavement!
|
|