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HNC Electrical and Electronic Engineering
Year One - 2013/14
Module: Programmable Logic Controllers

Programmable Logic
Controllers

Traffic Lights

Keith A
...
Hudson

2

PLCs
01 April, 2014

Contents
1

Design Brief
...
5

3

Specification
...
1

Traffic Control
...
1
...
6

3
...
2

All Stop
...
1
...
6

3
...
4

All Stop
...
1
...
7

3
...
7

4

Pedestrian / Traffic Interaction
...
11
5
...
11

5
...
11

5
...
11

5
...
11

6

Inputs
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12

8

Stage 1 Design
...
13

10

Instruction list
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35

12

Device Comment List
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37

14

Cross Reference List
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41

16

Operators Manual
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1

System Commissioning
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2

System Maintenance
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3

System Start-up
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43

18

Data Sheets
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44

HNC Electrical and Electronic Engineering

Year One: 2013/14

Keith A
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21

Appendix A
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Hudson

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PLCs
01 April, 2014

Figures
Figure 1: A typical traffic light installation at a cross roads (Findley, n
...
6
Figure 2: Sequencial Function Chart (SFC)
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42

Tables
Table 1: Normal operating sequence for UK traffic lights
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7
Table 3: Traffic and pedestrian interaction (Puffin crossing type)
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8
Table 5: Interaction between N-S, E-W traffic and pedestrians (when N-S has priority)
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10
Table 7: Input assignments
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12

HNC Electrical and Electronic Engineering

Year One: 2013/14

Keith A
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The program should control the
safe operation of traffic lights at a cross roads
...
This
must also operate in a safe manor for the pedestrians and vehicle drivers
...
(This is the available hardware
...


2 Assumptions
If the traffic lights to be controlled are on a UK highway they should follow the sequence defined in Table 1
...











RED & AMBER
Also means the vehicle
should stop behind the
white line, but they should
be prepared to go
...


AMBER

Vehicle should stop behind
the white line
...


The road layout is North-South (N-S) and East-West (E-W)
...

The system makes no allowances for variation in traffic flow at different times of day
...
e
...

Following each period of traffic flow, there will be a period of no flow (i
...
red light for all)
...

A Puffin Crossing will be implemented to allow pedestrians to cross the road
...
But pedestrians will only
be directed to cross when all traffic is stopped
...

Pedestrian will be given a set time to cross the road after which the green man will be extinguished
and the red man will be displayed
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Hudson


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PLCs
01 April, 2014

There will be no induction loops in the road and no cameras to detect the presence of vehicles or
pedestrians
...
A typical layout is shown in Figure 1
...
d
...
The initial state will be
Amber then RED for all traffic
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3
...
1
...

The E-W AMBER lights will be displayed
...
1
...


3
...
3







North-South traffic flow
The N-S RED lights will be displayed
...

The N-S RED and AMBER lights will be extinguished
...

After a set time the N-S GREEN light will be extinguished
...


3
...
4


All Stop
The lights in all four directions will display the RED stop lights
...
Hudson
3
...
5





PLCs
01 April, 2014

7

East-West traffic flow
The E-W RED and AMBER lights will be extinguished
...

After a set time the E-W GREEN light will be extinguished
...


Repeat steps 3
...
1 to 3
...
5

3
...
This will be implemented in accordance with
Highways Agency guidelines (Department for Transport, 2005)
...

The ‘Call Button’, Red-Man (don’t cross) and Green-Man (cross) (see Table 2) are all located on the nearside of the
crossing in accordance with PUFFIN Crossing design
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Hudson

PLCs
01 April, 2014

8

4 Pedestrian / Traffic Interaction
Table 3 shows how the function of the lights
...
The timings chosen for this particular implementation are shown in Table 4
...

Don’t
start
crossing

extendabl
e period

20-60

3

1-3

4-9

1-5

0-22

pedestrians

to finish
crossing

0-3

RED
MAN

RED
MAN

Vehicles
stop

Vehicles
stop

0-3

2

(Department for Transport, 2005)
For this system the following times will be used:
Table 4: Times to be used in each period

Period

Time (s)

Period

1
2
3
4
5

Time (s)

40
6
3
7
3
8
9
9
1
As our system does not have any pedestrian detection facilities periods 6, 7 and 8 will be 0 seconds
...


HNC Electrical and Electronic Engineering

Year One: 2013/14

Keith A
...
Hudson

PLCs
01 April, 2014

10

Table 6: between N-S, E-W traffic and pedestrians (when E-W has priority)

Period

Pedestrian
Crossing

N-S
Traffic Lights

E-W
Traffic Lights

Notes

1

Pedestrian
don’t cross

Stop

Go

East-West traffic flow
40 seconds

2

Pedestrian
don’t cross

Stop

Stop
warning

3 seconds

3

Pedestrian
don’t cross

Stop

Stop

Vehicle clearance period
3 seconds

4

Pedestrian
invitation to
cross

Stop

Stop

All stop – Pedestrians cross
9 seconds
(Only if crossing button
pressed)

5

Finish /
don’t start
crossing

Stop

Stop

1 seconds

6

Finish /
don’t start
crossing

Stop

Stop

Additional pedestrian clearance
period
0 seconds

7

Pedestrian
don’t cross

Stop

Stop

0 seconds

8

Pedestrian
don’t cross

Stop

Stop

0 seconds

9

Pedestrian
don’t cross

Stop, get
ready to
go

Stop

2 seconds

HNC Electrical and Electronic Engineering

Year One: 2013/14

Keith A
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5
...

No pedestrian crossing
...


This stage will be programmed and tested on the PC only
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2 Stage 2




Addition of a pedestrian crossing activated using an additional push-button
...

Green man to indicate that it is safe to cross
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5
...


This stage will be programmed and tested on the PC before being transferred to a PLC for Factory Testing
...
4 Future Enhancements





There should be multiple crossing push-buttons which should be wired separately so if one fails
others are available (redundancy)
...
This
again provides redundancy but also makes it easier for drivers to see a set of lights should their
view of the primary lights be obstructed
...


HNC Electrical and Electronic Engineering

Year One: 2013/14

Keith A
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This will be located in the roadside cabinet along with
the PLC
A push button to allow a pedestrian to indicate a desire
to cross the road
...
Hudson

PLCs
01 April, 2014

13

8 Stage 1 Design
Start PB
OR

State 4
AND
Timer 4
All Stop
N-S RED : Y10, Y30 on
E-W RED : Y20, Y40 on
Start timer 1

State 1
M1
State 1
AND
Timer 1

N-S Go
N-S GREEN : Y12, Y32 on
E-W RED : Y20, Y40 on
Start timer 2

State 2
M2
State 2
AND
Timer 2

All Stop
N-S RED : Y10, Y30 on
E-W RED : Y20, Y40 on
Start timer 3

State 3
M3
State 3
AND
Timer 3

East/West go
N-S RED : Y10, Y30 on
E-W GREEN : Y22, Y42 on
Start timer 4

State 4
M4

Figure 2: Sequential Function Chart (SFC)

Figure 2 show the SFC for the Stage 1 implementation
...


HNC Electrical and Electronic Engineering

Year One: 2013/14

Keith A
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Similarly, States 5 and 6 will be added between State 3 and State 4
...
Hudson

15

PLCs
01 April, 2014

10 Stage 3 Design
In order to implement the amber lights two new states are required for North-South and two more for East-West
...

Each entry in Table 5 and Table 6 corresponds to a single state in the SFC and therefore the ladder logic
...

Therefore an addition state to display North-South amber lights at system start up is required
...


HNC Electrical and Electronic Engineering

Year One: 2013/14

Keith A
...
Hudson

HNC Electrical and Electronic Engineering

17

PLCs
01 April, 2014

Year One: 2013/14

Keith A
...
Hudson

HNC Electrical and Electronic Engineering

19

PLCs
01 April, 2014

Year One: 2013/14

Keith A
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Hudson

HNC Electrical and Electronic Engineering

21

PLCs
01 April, 2014

Year One: 2013/14

Keith A
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Hudson

HNC Electrical and Electronic Engineering

23

PLCs
01 April, 2014

Year One: 2013/14

Keith A
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Hudson

HNC Electrical and Electronic Engineering

25

PLCs
01 April, 2014

Year One: 2013/14

Keith A
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Hudson

HNC Electrical and Electronic Engineering

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PLCs
01 April, 2014

Year One: 2013/14

Keith A
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Hudson

HNC Electrical and Electronic Engineering

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PLCs
01 April, 2014

Year One: 2013/14

Keith A
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)

HNC Electrical and Electronic Engineering

Year One: 2013/14

Keith A
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Hudson

HNC Electrical and Electronic Engineering

32

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01 April, 2014

Year One: 2013/14

Keith A
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Hudson

34

PLCs
01 April, 2014

(The instruction list was output from GX Developer as a PDF then converted to JPEGs
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Hudson

35

PLCs
01 April, 2014

13 Timer Setting Values List

(This list was output from GX Developer as a PDF then converted to JPEGs
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Hudson

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PLCs
01 April, 2014

14 Device Comment List

(This list was output from GX Developer as a PDF then converted to JPEGs
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Hudson

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PLCs
01 April, 2014

15 Device Use List

(This list was output from GX Developer as a PDF then converted to JPEGs
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Hudson

38

PLCs
01 April, 2014

16 Cross Reference List

HNC Electrical and Electronic Engineering

Year One: 2013/14

Keith A
...
Hudson

40

PLCs
01 April, 2014

(This list was output from GX Developer as a PDF then converted to JPEGs
...
Hudson

41

PLCs
01 April, 2014

17 Electrical / Mechanical Drawings
Not required
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Hudson

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PLCs
01 April, 2014

18 Operators Manual
18
...

Display “No Traffic Lights” signs (see Figure 4) on all lighting posts
...

Power up the PLC and ensure no warning or fault LEDs are displayed
...

Ensure all sets of traffic lights are now showing (STOP) RED lights
...

Check the lights are still operating in the correct sequence, over an extended period of time
...
For the remainder of the working day perform hourly checks
...

Record all results in the Site Acceptance Test result document
...
2 System Maintenance
For maintenance (planned or otherwise) expected to last 30 minutes or more OR for highways with a high volume of
traffic:
Control of traffic flow should be performed by an alternative method (e
...
Stop-Go signs, temporary traffic
lights, etc
...

Once traffic flow is under external control, the system may be powered off by pressing the RUN/STOP button
on the PLC
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Hudson

43

PLCs
01 April, 2014

If work on the PLC is to be carried out it must be isolated from the Mains Power FIRST
...
3 System Start-up
If the system is turned off for any reason (maintenance, repair, power failure, etc
...

Open the road-side control panel
...

Press the RUN/STOP button on the PLC and ensure no warning or fault LEDs are displayed
...
g
...

Hold down the Start push-button for five (5) seconds
...

Observe the lights for one complete cycle to ensure everything is operating correctly
...

Once normal traffic flow has been established, close the control panel and LOCK IT
...
The following checks shall be performed:
1
...

3
...


Ensure the correct lighting sequence occurs for every set of lights
...

Ensure all bulbs are working correctly
...
This will be defined in the data sheet
for the bulb as the Mean time to failure (MTTF), normally expressed in hours
...

5
...


20 Data Sheets
Not required
...
Hudson

44

PLCs
01 April, 2014

21 Conclusion
Developing this program in incremental stages had a number of benefits:













The initial design was relatively simple and easily manageable
...

The first stage required only a few distinct states
...

The main advantage is that a (partial) working program is produced rapidly
...
(It would be much more costly if changes needed to be incorporated
into the final program
...
As the PLCs are at college I would only have been able to test
the program at college, for a couple of hours, one day a week
...

Usually in software development, much of the initial work is not performed on the target hardware
...

As actual traffic lights / pedestrian crossing were unavailable to connect to the PLC, testing would
not have been possible without the monitoring facility available in GX Developer
...


There were however some drawbacks to this method:




In the first iteration of my program I used states M1, M2, M3 and M4
...
Although the PLC doesn’t care what the actual numbers are, it ‘looks’ wrong and may
potentially be confusing to maintenance programmers in the future
...
This would leave
‘space’ for four extra states in between the initial states
...
(At the
moment I don’t have the knowledge or the time to do this
...
The
states could, therefore, all be allocated the correct sequential numbers
...


HNC Electrical and Electronic Engineering

Year One: 2013/14

Keith A
...
, n
...
Highway code - Road junctions - highway code
...
findleys
...
uk/highway_code/road_junctions
...

Melore, P
...
Your Personal PLC Tutor-Learn PLC Programming Here
...
[Online]
Available at: http://www
...
net/qanda/showthread
...

Mitsubishi Electric, 2010
...
[Online]
Available at: https://my
...
com/downloads_manager
...


HNC Electrical and Electronic Engineering

Year One: 2013/14

Keith A
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1 General Arrangement
7
...
1 Puffin crossings use near-side pedestrian signal heads and an extendable all-red crossing period which is
instigated by a push button request accompanied by a pedestrian detector demand
...

7
...
2 Puffin crossings have two forms of detection for pedestrians
...
These cancel pedestrian demands which are no longer required
...
These extend the all-red time, Period 5
...
2 Timings
The Operational Cycle use and variations are described in Table 5 and timings in Table 6
...

The delay time, after which the call is cancelled if the kerb-side detector does not detect a pedestrian, should be set
to a value between 2 and 4 seconds depending on site conditions
...
Exceptionally this may be adjusted for site conditions
between the limits of 6 to 15 seconds
...
Only in exceptional
circumstances should a value greater than 30 seconds be used
...

 The maximum period will normally start at the pedestrian demand but may start at the
commencement of the vehicle green (‘pretimed max
...
p
...
• it will terminate, subject to a pedestrian demand, either at the end of the
minimum time; when a gap is detected in traffic (gap change); or on the expiry of the preset
maximum time (forced change)
...


Period 2
This is the mandatory 3 second stopping amber signal to vehicles
...
p
...
, this period will be 3 seconds
...


Period 4
The timing for the Pedestrian green walking figure period, with the option of the audible and/or tactile signal, should
normally be set to 4 or 5 seconds at crossings with light to moderate pedestrian flows
...

 areas where there is a higher proportion of disabled or elderly people
...
Hudson

PLCs
01 April, 2014

47

Period 5
The all-red period of 1-5 seconds
...
The extension period for the pedestrian oncrossing detector should normally be set within the range 1
...
2 seconds
...
The duration of this period is
normally 3 seconds but can be adjusted between 0-3 seconds
...
67 (the length of crossing - 3
metres)
...
Normally set
to 0 seconds but can be adjusted in steps of 1 second to a maximum of 3 seconds
...


Table 5 PUFFIN CROSSINGS - OPERATIONAL CYCLE, USE & VARIATIONS
PERIOD USE

VARIATION FOR

1

Vehicle running time

Traffic volumes

2

Standard amber to vehicles

None

3

Vehicle clearance period

Vehicle actuation

4

Pedestrian invitation to cross

Road width, disabled pedestrians, crossings with
central refuge

5

Pedestrians must not start to cross

Type of detector

6

Completion of pedestrian crossing time

Road width

7

Additional pedestrian clearance time

Pedestrian detection

8

Additional pedestrian clearance time

Pedestrian gap change

9

Standard red/amber to vehicles

None

HNC Electrical and Electronic Engineering

Year One: 2013/14

Keith A

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