1. NEW TECHNOLOGY
Intelligent Wireless Traffic Signal Controller
Why Dig Roads
If you can install them in air?
C-DAC Thiruvananthapuram has deployed Wi-TraC, a wireless traffic signal controller developed by it, at one of the
busy junctions in Thiruvanthapuram on a trial basis. If this proves successful, the problems posed by the conventional
traffic signal controllers might become a thing of the past.
C
-DAC Thiruvananthapuram has developed a 2’x 2’x 3’ pedestal on the pavement. This normally
Wireless Traffic Signal Controller (Wi-TraC) obstructs pedestrian movement. Further, in a con-
with distinct advantages over conventional ventional traffic controller all the signal lamps or
traffic signal controllers. The impetus for developing poles are physically linked to the control electronics
the Wi-TraC has been the increasing problems with through copper cables. This requires digging one-
conventional controllers. Due to the tremendous in- foot wide and one-and-a-half foot deep ducts across
crease in vehicles, number of roads and the number the road from the traffic controller equipment to
of road intersections, the need for traffic controllers the signal poles, installing Hume pipes in the ducts
is increasing every day. But installing conventional, and pulling multi-core armoured cable through the
wired traffic controllers is difficult for the agencies pipes. Often, this process damages good roads, se-
involved. riously affecting their life span. Disturbance to road
users, both drivers and pedestrians, and possibil-
The traditional way of installing conventional traf-
ity of damaging other utilities such as telephone
fic controllers is to mount the controller box on a
cables, electric cables and water lines are other
2 TrafficInfraTech • December ’11 - January ’12 • www.trafficinfratech.com

2. NEW TECHNOLOGY
Controller
Hume Pipe
Armoured
Cable
Figure 3: Traditional
way of installing Traffic
Signal Controllers
Figure 1: Conventional Traffic Signal Controller installed on the pavement
hazards. Added to this is the fact that The Wi-TraC wireless traffic controller, features, energy efficiency and size.
digging of roads during monsoon is often developed with funding from Department Since it is small and pole mountable, it
very difficult, if not impossible. Acquiring of Technology (DIT), eliminates most of does not occupy any space on the pave-
permissions from various local authorities these problems. It is an Area Traffic Con- ment. It is in fact a cost effective solution
for digging the roads is another hurdle. A trol System (ATCS) compatible Vehicle for all the issues listed above – no dig-
principal reason for the high cost of install- Actuated (VA) road traffic signal control- ging, no Hume pipes and no armoured
ing conventional traffic signal controllers is ler, the most sophisticated of its class. It cables. The Wi-TraC is designed to oper-
the extensive digging and cable work re- has many advantages over conventional ate on solar power. It has GPS enabled
quired. traffic controllers in terms of functional Real-time Clock (RTC) for distributed
time synchronisation. The result is easy
installation, high availability (no cable
Figure 2: Wi-TraC Master and Slave Controller installed on signal poles
faults or RTC corruption) and less cost
of installation.
The Wi-TraC is a 32-bit microcontroller-
based intelligent road traffic controller
with a distributed architecture. It consists
of a master controller and a number of
slave controllers. The traffic junction plan
resides in the master controller. Every is-
land or signal pole has a slave controller.
The signal lamps are driven from the mas-
ter controller and the slave controller of
the respective signal poles. The number of
slave controllers required depends on the
junction geometry, e.g. for a four-arm traf-
fic intersection, one master controller and
three slave controllers will be required. The
Wi-TraC can support up to 16 slave con-
trollers. The master-slave communication
is done on the 2.4 GHz license-free band.
In situations where signals are jammed on
the 2.4GHz band, the Wi-TraC automati-
cally switches to the backup frequency of
868MHz that is also license-free.
www.trafficinfratech.com • December ’11 - January ’12 • TrafficInfraTech 3

3. NEW TECHNOLOGY
Figure 4: Damaged
The Wi-TraC user interface contains a
pavement due to 20x4 LCD display and a 5x4 keypad. Traf-
traffic signal fic plan data is entered through the user
installation
interface or with a laptop or, if networked
to the traffic monitoring centre, down-
loaded from the remote computer. Wi-TraC
has 16 optically isolated vehicle detector
interfaces compatible with both inductive
loop detection and camera based virtual
loop detection – the most common meth-
ods of vehicle detection. The GPS enabled
RTC ensures accurate real-time clock to
synchronise with the adjacent intersec-
tion controller. Police personnel can use
the wireless police panel interface to put
the traffic lights at the intersection in flash
mode, manual mode and hurry call mode
or they can even turn off the lights with
a hand-held remote control. The Wi-TraC
supports PC interface for reading and writ-
ing plans and configurations. It is also pos-
sible to do the plan editing remotely from
the ATCS.
The Wi-TraC consumes significantly less
power than solar powered conventional traf-
fic controllers too because it operates on 12V
DC whereas conventional controllers operate
on 24V DC. The size of the Wi-TraC panel
is also much smaller as a consequence. An-
other important feature of the Wi-TraC is its
ability to control intensity of the signal lamps
through Pulse Width Modulation (PWM).
Luminosity designed for daytime, operation
of signal lamps can be quite disturbing for
motorists during night. But with the Wi-
TraC, the intensity of the signal lamps can
be decreased during night as they can be
programmed to operate with different signal
intensities depending on the ambient light.
This also helps in saving a significant amount
of power. Moreover, since Wi-TraC does not
use armoured cable for interconnecting the
master controller and the signal heads, an
average saving of 30% to 40% in civil work,
Figure 5: Wireless and laying of cables, pipes and conduits has
Traffic Controller
Architecture
been envisaged compared to the convention-
al traffic signal installation.
For switching the signal lamps, the mas- packets, the master controller retransmits
Modes of Operation
ter controller establishes communication the commands. When the master control-
link with the slave controllers by sending ler fails, all slaves go into Flashing Yellow The Wi-TraC supports the following
wireless ping commands. An acknowledge- mode after a preset time-out period. In modes of operation
ment received from the slave controller in- case of failure of any slave controller, all
Fixed: The input signals from the vehicle
dicates that the link has been established. other slaves and the master go into Flash-
detection system are ignored in this mode.
The master controller then sends informa- ing Yellow mode and this information is
The controller will operate with fixed time
tion of the lamp outputs to the slave con- logged locally as well as sent to the remote
periods from the timetable. The controller
troller whenever a stage change occurs. server (if linked to the traffic monitoring
always starts from Stage 1 on restart.
The slave controller decodes the logic and centre) for taking action. All packets of
switches on the lamp as per the pattern communication are encrypted by 128 bit Vehicle Actuated: The Vehicle Actuated
of commands received. In case of dropped AES (Advanced Encryption Standard). strategy allocates green time to a running
4 TrafficInfraTech • December ’11 - January ’12 • www.trafficinfratech.com

4. NEW TECHNOLOGY
phase within the constraints of a fixed mini- The Vehicle phase contains three signal plan time or on hardware failure will force
mum and maximum green time setting for aspects, viz. red, amber and green. The the signals into Flashing Amber.
the phase. This depends on the real-time termination of vehicle phase is always with
Start Amber Plan: The Start Amber is a
demand reported by the vehicle detectors. amber. The sequence of signal switching
programmable interval for a period of five
With fully actuated control, all signal phases is red-green-amber-red. The Pedestrian
to 10 seconds. The Start Amber executes
are actuated and all signalised movements phase contains two signal aspects, viz.
the Flashing signal for the programmed
require detection. red and green. The termination of pedes-
interval followed by All Red when the Wi-
trian phase can be either red flash or green
ATCS: The controller will execute the sig- TraC powers up.
flash. The sequence of signal switching is
nal timing proposed by the ATCS server.
red-green-red flash or green flash-red. Red Extension Plan: When a right-of-
Coordinated (Cable-less): The Cable- way is terminated, opening of the next right-
The Filter green phase provides signal
less Linking Facility allows a method of co- of-way is delayed by a time period called
for the right turning traffic. When linked
ordinating traffic signals along a route and/ Red Extension. With no continuing phase,
with a vehicle phase the termination of fil-
or in an area using timing information. The this gives an effect of all red between stage
ter green is blackout. Otherwise, it flashes
Distributed Time Synchronisation (DTS) is changes. The Red Extension gives an ad-
for a few seconds before termination. The
achieved by GPS enabled Real-time Clock ditional clearance time after the Amber. The
Indicative green phase is a continuously
in the controller. Red Extension is a programmable period of
flashing signal which provides signal for
zero to five seconds.
Manual: Manual operation of the traffic the left turning traffic. The termination of
signal stage sequence is required to cater indicative green is always blackout. The Wi-TraC keeps an error log and reports
to situations such as abnormal congestion, error like lamp failure, output short circuit,
Dummy Phase is a filter to manage the
accidents, breakdowns and other special green-green conflict, detector failure, com-
lane change at the detection zone in Ve-
occasions. In Manual mode the stages ap- munication failure and power failure. Both
hicle Actuated mode of signal operation.
pear in the order specified in the timetable Master and Slave controllers are pole mount-
This is not associated with any signal lamp
with time periods defined by the person able in IP65 compliant cabinet. The system
but the signal timing is based on the detec-
manning the junction. provides easy access to the user interface
tion input to the Dummy phase.
and control electronics for enhanced service-
Hurry Call: The purpose of Hurry Call is
32 – Stage Plan: A stage can primar- ability. Provision to house vehicle detectors
to give prioritised right of way to certain
ily be considered as a condition of traffic inside the cabinet is also available.
vehicles on demand. A maximum of four
lights during a period of the cycle, which
hurry calls can be predefined in the sys- The trial results have been favourable
gives right-of-way to one or more traffic
tem, and are activated through switches and satisfactory for using Wi-TraC in 24x7
movements.
on the police control panel. operations. C-DAC also plans to install Wi-
24 - Cycle Plan: Cycle is a scheme in TraC at Pune in the near future.
Flash Mode: In the Flash mode, selected
which stages are given some fixed order.
lamps are made to flash. The lamps can
be amber, red or a combination of both. 20 - Day Plan: Day Plan is the distribu-
This mode can be selected either through tion of cycle plans for a particular day.
timetable or by control switch.
4 - Week Plan: Week Plan is the distri-
Signal Plans bution of available day plans for a week.
The Wi-TraC supports various signal 20 - Special Day plan: Holidays fall-
P Ravikumar
plans as listed below: ing on normal weekdays can be treated
Joint Director, CDAC
as special days and can have a different
32 - Phase Plan: A Phase is a right-of- Thiruvananthapuram
day plan, selected from the available day
way signal that is defined by one, two or
plans.
three signal lights.
All Red Plan: A condition when only
S. Phase Symbol No. of red aspects are displayed. The All Red is
Group
No Type Lamps executed when an abrupt signal change R Prakash
1 Vehicle V 3 × × ×
is required (e.g. power up, flash-to-signal,
Senior Engineer, CDAC
manual-to-auto, hurry call-to-auto, etc).
This is a programmable interval from 0 to Thiruvananthapuram
2 Pedes- P 2 × ×
trian 5 seconds.
3 Filter F 1 × Conflict Plan: Any two phases that are (The authors wish to acknowledge the valu-
Green able help received from the Department of In-
not allowed simultaneously are defined as formation Technology, Ministry of Communica-
4 Indicative I 1 × conflicting phases. The Conflict plan is a tions & Information Technology, Govt. of India,
Green listing of all conflicting groups. The system Traffic Signals Division, KELTRON, Trivandrum
supports listing of all possible conflicting and Thiruvananthapuram Road Development
5 Dummy D 0
Company Limited (TRDCL) in the development
phases. A conflict detected either at the of Wi-TraC).
www.trafficinfratech.com • December ’11 - January ’12 • TrafficInfraTech 5