SIST EN 50556:2011

SLOVENSKI STANDARD
01-december-2011
1DGRPHãþD
SIST HD 638 S1:2002
SIST HD 638 S1:2002/A1:2007
Sistemi prometne signalizacije
Road traffic signal systems
Straßenverkehrs-Signalanlagen
Systèmes de signaux de circulation routière
Ta slovenski standard je istoveten z: EN 50556:2011
ICS:
93.080.30 Cestna oprema in pomožne Road equipment and
naprave installations
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 50556
NORME EUROPÉENNE
February 2011
EUROPÄISCHE NORM
ICS 93.080.30 Supersedes HD 638 S1:2001 + A1:2006

English version
Road traffic signal systems
Systèmes de signaux de circulation Straßenverkehrs-Signalanlagen
routière
This European Standard was approved by CENELEC on 2011-01-02. CENELEC members are bound to
comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and
notified to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia,
Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania,
Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Management Centre: Avenue Marnix 17, B - 1000 Brussels

© 2011 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
-
Ref. No. EN 50556:2011 E
Foreword
This European Standard was prepared by CENELEC Task Force BTTF 69-3, Road traffic signal systems.

The text of the draft was submitted to the Unique Acceptance Procedure and was approved by CENELEC as
EN 50556 on 2011-01-02.
This document supersedes HD 638 S1:2001 + A1:2006.

The main changes with respect to HD 638 S1:2001 + A1:2006 are the following:

− update of the normative-references;

− editorial revision;
− reduction of the classes;
− adaptation to the level of technology.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN and CENELEC shall not be held responsible for identifying any or all such patent rights.
The following dates were fixed:

– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2012-01-02

– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2014-01-02

__________
- 3 - EN 50556:2011
Contents
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Electrical supply and limits . 10
4.1 Nominal voltages . 10
4.2 Operating voltage range . 10
4.3 Low voltage . 11
4.4 Overvoltage . 11
4.5 Voltage dip . 11
4.6 Mains frequency . 11
5 Safety . 12
5.1 Electrical safety . 12
5.2 Traffic safety . 14
6 Testing . 19
6.1 General . 19
6.2 Organisation of testing . 19
6.3 Environmental tests . 20
6.4 Electrical tests . 22
6.5 Electrical safety tests . 23
6.6 Traffic safety tests . 24
6.7 Electromagnetic compatibility testing . 25
7 Electrical interfaces . 26
7.1 General . 26
7.2 Detector interface . 26
8 Installation . 26
8.1 General . 26
8.2 Tests carried out during installation . 26
8.3 Test of cables following the installation of cables . 27
8.4 Inspection of terminations following the installation and termination of all equipment and cables . 27
8.5 Test of impedance . 27
8.6 Insulation of live parts to earth . 28
8.7 RCD (residual current detector / earth leakage breaker) . 28
8.8 Fuses . 28
8.9 Voltage and polarity of supply . 28
8.10 Connections between controllers, signals and ancillary equipment . 29
8.11 Safety covers . 29
8.12 Functional check of road traffic signal systems . 29
9 Maintenance . 29
9.1 General . 29

9.2 Types of maintenance . 29
9.3 Documentation required for maintenance . 29
9.4 Equipment not covered by this standard . 30
9.5 Safety testing procedures . 30
9.6 Maintenance testing procedures . 30
10 Marking and labelling . 32
11 Classification of environmental test conditions . 33

Figure
Figure 1 − Failure consideration of a Road Traffic Signal System − Protection against accidents caused by
technical failures .18

Tables
Table 1 − Classification according to voltage dip .11
Table 2 − Requirements for maintenance measures (intervals (PTI) in months) .31
Table 3 − Environmental testing .33

- 5 - EN 50556:2011
Introduction
To satisfy the legal and regulatory requirements and specific provisions of each CENELEC country, certain
characteristics in this standard contain a range which is defined by a number of discrete classes. The class to
be used in the country will be selected by the Standards Authority of the CENELEC member of that country
from the range specified.
Thus this European Standard contains the essential electrotechnical requirements of all CENELEC countries
and permits through the class selection procedure, countries to incorporate their own requirements.
It is believed that this first step will allow, over a period of time, a gradual alignment of Road Traffic Signal
Systems in Europe.
1 Scope
This European Standard specifies requirements for Road Traffic Signal Systems, including their
development, design, testing, installation and maintenance.
In particular, it forms the electrotechnical part of the following two standards issued by CEN:
– EN 12368, Traffic control equipment ― Signal heads
– EN 12675, Traffic signal controllers ― Functional safety requirements
Each of these standards above should be used with this standard either singly or together to define an
operational equipment or system. This should be achieved by using the electrotechnical methods and testing
defined in this standard.
Where Road Traffic Signal Systems are to be used with other systems, e.g. public lighting or railway
signalling and communication, this standard should comply with the other respective standard to ensure that
overall safety is not compromised.
Only permanently or temporarily installed Road Traffic Signal Systems are included in this standard. Central
office and portable signalling systems are not covered.

2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.

EN 12368 Traffic control equipment - Signal heads
EN 12675:2000 Traffic signal controllers - Functional safety requirements
EN 50102 Degrees of protection provided by enclosures for electrical equipment against
external mechanical impacts (IK code)
EN 50110-1 Operation of electrical installations
EN 50129 Railway applications - Communication, signalling and processing systems - Safety
related electronic systems for signalling
EN 50293 Electromagnetic compatibility - Road traffic signal systems - Product standard
EN 60529 Degrees of protection provided by enclosures (IP Code) (IEC 60529)
EN 60950-1:2006 Information technology equipment - Safety - Part 1: General requirements
(IEC 60950-1:2005, mod.)
EN 61008 series Residual current operated circuit-breakers without integral overcurrent protection
for household and similar uses (RCCB's) (IEC 61008 series)
EN 61009 series Residual current operated circuit-breakers with integral overcurrent protection for
household and similar uses (RCBO's) (IEC 61009 series)
EN ISO 9001:2008 Quality management systems - Requirements (ISO 9001:2008)
HD 384.4 series Electrical installations of buildings - Part 4: Protection for safety (IEC 60364-4
series)
HD 60364-5-54 Low-voltage electrical installations - Part 5-54: Selection and erection of electrical
equipment - Earthing arrangements, protective conductors and protective bonding
conductors (IEC 60364-5-54)
EN 60068-2-1 Environmental testing - Part 2-1: Tests - Test A: Cold (IEC 60068-2-1)
EN 60068-2-2 Environmental testing - Part 2-2: Tests - Test B: Dry heat (IEC 60068-2-2)
EN 60068-2-5 Environmental testing - Part 2: Tests - Test Sa: Simulated solar radiation at ground
level (IEC 60068-2-5)
- 7 - EN 50556:2011
EN 60068-2-14 Environmental testing - Part 2-14: Tests - Test N: Change of temperature
(IEC 60068-2-14)
EN 60068-2-30 Environmental testing - Part 2-30: Tests - Test Db: Damp heat, cyclic (12 h + 12 h
cycle) (IEC 60068-2-30)
EN 60068-2-64 Environmental testing - Part 2-64: Tests - Test Fh: Vibration, broadband random
and guidance (IEC 60068-2-64)
EN 61140 Protection against electric shock - Common aspects for installation and equipment
(IEC 61140)
CLC/TS 50509 Use of LED signal heads in road traffic signal systems
IEC 60050-191 International Electrotechnical Vocabulary - Chapter 191: Dependability and quality
of service
IEC 60050-826 International Electrotechnical Vocabulary - Part 826: Electrical installations
IEC 60183 Guide to the selection of high-voltage cables
IEC 60417 (database) Graphical symbols for use on equipment

3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1 General
3.1.1
Road Traffic Signal Systems
include systems and devices, provided they are affiliated to them in terms of circuitry

NOTE They may consist of the following elements which is not in itself a complete list:
– Controllers;
– Signal heads, signalling devices and traffic signs
e.g. signal heads for traffic signals;
acoustic signal generators;
mechanical signal generators;
traffic signs connected to the Road Traffic Signal System;
– Traffic sensors and detectors
e.g. request push buttons;
vehicle detectors / Pedestrian Detectors;
– Monitoring equipment
e.g. photographic monitoring devices;
– Equipment Enclosures;
– Electrical Supply;
– Cables;
– Interconnections;
– Supports.
3.1.2
Failure Mode Analysis
means of examining all failure modes to ensure that signal states endangering the road users and/or risk of
electrical hazard cannot occur during normal conditions of operation of a Road Traffic Signal System or if
they do occur as a result of or whilst a failure (failure mode) exists that they signal states endangering the
road users are detected and prevented from continuing

3.1.3
Signal Safeguarding Facility
facilities intended to prevent states of signals endangering the traffic

3.1.4
monitoring element
device that signals electrical and mechanical states of equipment, preferably for signal circuits, and which
converts the obtained information in such a manner that it can be processed in signal safeguarding facilities

3.1.5
hardware
complete Road Traffic Signal System or a (material) part of it

3.1.6
hardware fault
failures of components and any influence that will cause the equipment to fail
NOTE Systematic hardware faults constitute either design faults or systematic production faults.

3.1.7
software
all or part of the sequence instructions for a Road Traffic Signal System including the affiliated documentation
NOTE Software is exclusively immaterial, so that it is subject to no wear or failure mechanisms. Once implemented, software
cannot be falsified on its own.

3.1.8
software error
deviation between the realised and intended functional contents of the software
NOTE All errors in the software are systematic errors. They are caused by:
– invalid specification (incorrect formulation of intention);
– incorrect programming (incorrect translation of the specification to sequential instructions).
Apparent program falsification in memories is produced by hardware faults or failures or is caused by inadmissible influencing.

3.2 Traffic engineering
3.2.1
controllers (traffic)
electrical device to control signals

3.2.2
signal group
sequence of conditions applied to a group of signal heads, which always received identical signal light
indications
3.2.3
Operating System
principle software that allows a computer to operate, and which establishes the basic foundations, protocols
and functions that the computer can perform, including communication with internal and external resources

3.2.4
Application Program
software that determines specific tasks that a computer can perform, i.e. operate as a traffic controller

NOTE Application software rests on and extends the capabilities of the operating system to meet customer needs.

3.2.5
Traffic Data
data which specifies how the application program will perform in the particular circumstances of one traffic
system
NOTE This may be considered to be in two parts.

3.2.5.1
Traffic Safety Data
- 9 - EN 50556:2011
all Traffic Data stored in non-volatile memory that has a direct impact on the safety of road users

3.2.5.2
Traffic Non Safety Data
all the remainder of the data which will not cause an unacceptable danger to the road user if the data is
changed
3.2.6
Design Authority
Design Responsible
individual or group (organisation) responsible for the safe design and manufacturing, including the
instructions for safe use, installation and maintenance of the equipment or system

3.3 Electrotechnical
3.3.1
live part
see IEC 60050-826
3.3.2
enclosure (EN 50102)
part providing protection of equipment against certain external influences and, in any direction, protection
against contact
NOTE This definition from the existing International Electrotechnical Vocabulary (IEC 60050-826) needs the following explanations
under the scope of this standard:
a) Enclosures provide protection of equipment against harmful effects of mechanical impacts and protection of persons and
livestock against access to hazardous parts.
b) Barriers, shapes of openings or any other means - whether attached to the enclosure or formed by the enclosed equipment -
suitable to prevent or limit the penetration of the specified test probes are considered as part of the enclosure, except when
they can be removed without the use of a tool.

3.3.3
complete protection
protection that achieves:
a) effective and durable prevention of contact with live parts by the attachment of obstacles at least
conforming to type of protection IP2x as defined in EN 60529;
or
b) complete enclosure of live parts by insulating material that can be removed only by destruction (protection
by insulating envelopment)
3.3.4
partial protection
protection that prevents the possibility of accidental contact by persons or by objects usually handled by them
in one of the following ways:
a) by placing live parts at a distance that the possibility of accidental contact by persons or objects usually
handled by them is excluded (protection against accidental contact by a safety clearance);
or
b) by attaching obstacles conforming at least to type of protection IP1x as defined in EN 60529 (protection
against accidental contact by the attachment of obstacles)
3.3.5
reinforced insulation
see EN 60529
3.3.6
nominal voltages
see IEC 60050-826
3.3.7
earthed systems
see IEC 60050-826
3.3.8
Class 0 equipment
see EN 61140
3.3.9
Class I equipment
see EN 61140
3.3.10
Class II equipment
see EN 61140
3.3.11
Class III equipment
see EN 61140
3.3.12
safety extra-low voltage
SELV
see EN 61140
3.3.13
protective conductor (symbol PE)
see IEC 60050-826
3.3.14
earthing conductor
see IEC 60050-826
3.3.15
RCD
see EN 61008 series and EN 61009 series

3.3.16
voltage dip
see IEC 60050-161
3.3.17
insulation
see EN 60950-1:2006, 1.2.9
4 Electrical supply and limits
4.1 Nominal voltages
The standard nominal voltage for connection to the public supply shall be taken to be 230 V AC . Other
r.m.s
nominal voltages shall be permitted.
4.2 Operating voltage range
The system shall be classified according to its mains voltage range within which the Road Traffic Signal
System shall work as defined by EN 12675, as follows:
nominal voltage - 13 % .+ 10 %
The system shall not display signals which contravene EN 12675 when the supply voltage is outside the
above voltage ranges.
- 11 - EN 50556:2011
4.3 Low voltage
4.3.1 Auxiliary state switch response voltage (V )
aux
It is expected that all controllers will have a point where low input supply voltage will mean that the monitoring
systems employed may be unable to operate and therefore would be unable to guarantee the detection or
prevention of signal states which endanger traffic. The controller shall be prevented from reaching this limit
and should switch to a safe state (see Note), in a controlled manner before this point is reached.

In a controlled manner means that it shall shut down in such a way as to prevent any likelihood of a
hazardous signal state being displayed during the process of switching to the safe state.

NOTE The safe state noted above may either be all signals off or a flashing display of either red or yellow or a combination of red and
yellow, which is recognised in the country in which the controller is to be used as a safe state, warning users to proceed carefully / give
way to others.
4.3.2 Power up activation voltage
The system shall become active when the supply voltage reaches a value within its operating voltage range.
The restart procedure shall normally be automatic or in exceptional circumstances it may be by manual or
remote control. No signalling state dangerous to traffic shall be possible and the signalling state shall conform
to EN 12675.
4.4 Overvoltage
The system shall be classified as follows according to whether or not a protective device is incorporated
which cuts off the supply voltage to prevent damage. Where incorporated, the protective device shall operate
when the supply voltage is greater than the operating voltage range.
– Class D0: no protective device is required;
– Class D1: a protective device is required to provide protection up to 1 500 V .
r.m.s
4.5 Voltage dip
The system shall be classified according to the duration of dips in supply which affect the operation. In order
to avoid undesirable reactions by the signal safeguarding facilities, the system shall operate as shown in
Table 1 according to the duration of the voltage dip below V .
aux
Period t is a timeperiod of a voltage dip in the supply which will not affect the normal operation of the system.
Period t is a timeperiod of voltage dip in the supply when the system shall change to signals OFF followed by
the start up sequence.
Table 1 − Classification according to voltage dip
Criterion Values
ms
Period t < 20
Period t > 100
For any voltage dip in the supply between t and t the controller may remain working correctly or change to
1 2
signals OFF followed by the start up sequence.

4.6 Mains frequency
The system shall be classified as follows according to the acceptable variations in mains frequency:
50 Hz ± 4 %
5 Safety
5.1 Electrical safety
5.1.1 General
5.1.1.1 Introduction
The Road Traffic Signal System shall conform to HD 384.4 series. This subclause deals with the additional
requirements for Road Traffic Signal Systems.

5.1.1.2 Criteria − Leakage current
5.1.1.2.1 Road Traffic Signal Systems
Class T1:
For Road Traffic Signal Systems, leakage current protection facilities conforming to HD 384.4.41 shall be
fitted. Earth leakage circuit breakers conforming to EN 61008 series for nominal currents 20 % greater than
the expected current and nominal leakage currents ≤ 0,3 A shall be installed.
Class T2:
No requirement for leakage current protection facilities for the whole system, however the customer may
request facilities as class T1.
5.1.1.2.2 Maintenance equipment supply
To conform with HD 60364-4-41, an earth leakage circuit breaker conforming to EN 61008 series with
nominal leakage currents ≤ 0,03 A shall be installed.

5.1.1.3 Earthing
5.1.1.3.1 General
This subclause applies to the installation or part of the installation which is class I conforming to EN 61140.

5.1.1.3.2 Protective earth conductor (PE)
The system shall conform to HD 60364-5-54.
Protective earth conductors shall connect together all conductive parts and the PE terminals throughout the
system. They shall either be created by conductors in a cable or by separately installed wires and/or
construction parts.
In controllers the PE conductors shall be connected to the PE terminal / earth bus bar.
NOTE Metallic bodies which, by virtue of their location or smallness, cannot be touched or are unlikely to become live should be
designated excluded devices, i.e. they need not be connected to the PE conductor.
5.1.1.3.3 PE wiring of external equipment
NOTE 1 Examples of external equipment are poles, signal heads and detectors.
The system shall be classified according to the following methods.
Accessible conductive parts shall be connected to the PE conductors incorporated in the cables or a separate
PE cable.
NOTE 2 Armouring of cables may also be used as PE conductors where the cable construction permits.

5.1.1.4 Enclosure
The enclosure shall provide the mechanical protection to IK07 (see EN 50102) with the following criteria:
No damage shall occur to the equipment contained within the enclosure and the equipment shall continue to
operate to its specification. There shall be no degradation of the IP rating of the equipment.
Class V1:
Enclosures shall provide protection to IP44. When the manual panel is open, the protection provided shall be
to IP42. When the enclosure is open the protection shall be to IP20.
Class V2:
Enclosures shall provide protection to IP54. When the manual panel is open, the protection provided shall be
to IP23. When the enclosure is open the protection shall be to IP21.

- 13 - EN 50556:2011
5.1.1.5 Access
Covers, doors, flaps, or similar allowing access to controls, circuits or live parts when opened, shall be
capable of being opened only with the aid of a key or a tool. Keys may be specified either on a country basis
or by the customer.
5.1.1.6 Over-current protection
Supply voltages within the enclosure or external to the enclosure shall have excess current protection,
generally in accordance with HD 384.4 series.

5.1.1.7 Terminations
The system shall be classified according to its access to mains terminations as follows:
Class H0: No separate access to mains terminations.
Class H1: separate access to meters or parts of a mains terminal, etc.

5.1.2 Controller Signal outputs
The controller shall provide electrical power to the signals (as described in EN 12368), and the signals shall
use this power. Electrical details of compatible signal heads shall be specified by the controller manufacturer
in order to ensure the safety of the system. This should list either those signals know to be compatible or the
class of signals to EN 12368 or CLC/TS 50509 that would by definition make them compatible with the
control systems required monitoring performance and prevention of hazardous displays.

5.1.3 Interconnections
5.1.3.1 PE Terminal
The terminal points of the PE conductor on bodies shall be easily accessible and shall bear the identification
mark specified in IEC 60417. They shall provide bare metallic contact and serrated washers shall be used.
5.1.3.2 General terminations
The terminal points shall be of corrosion resisting materials.
5.1.4 Cables
5.1.4.1 PE cable dimensions
The minimum cross sections of PE conductors shall be as follows:
a) if part of a composite cable: the size of the largest conductor;
b) if laid in a protected manner: 2,5 mm copper;
c) if laid in an unprotected manner: 4,0 mm copper.
5.1.4.2 Earth cable dimensions
The minimum cross sections of earth conductors shall be as follows:
a) if corrosion protected: 16 mm copper or galvanised steel;
b) if corrosion unprotected: 25 mm copper;
50 mm galvanised steel.
5.1.4.3 Distribution cables
Distribution cables shall be designed to work in the environment found in traffic signal systems. They shall be
of adequate cross section to withstand fault currents which may occur under fault conditions.
NOTE This is dependent on the size of the protection device, the temperature range and the insulation material.
The rating voltage of cables carrying mains voltage shall be 1 000 V min. between conductors (this is the
value U as defined in IEC 60183 and is generally the second of the two values noted for a cable, U /U where
o
U is the maximum a.c. voltage between a conductor and earth and U is the maximum between conductors).
o
The number of cores specified for the installation will depend on the facilities required.

5.1.5 Insulation
5.1.5.1 Isolated circuits
In case of electrically isolated circuits: the insulation between the live parts of these circuits shall be
calculated for the higher operating voltage.
5.1.5.2 Linked circuits
In case of circuits linked in an electrically conductive manner and with different voltages: the calculation of the
reference voltage for the insulation between live parts shall be orientated to the highest operating voltage.
5.1.5.3 Insulation paths
5.1.5.3.1 General
For insulation paths EN 60950-1 applies, clearance and creepage distances and thickness of insulation see
EN 60950-1:2006, 2.10.
5.1.5.3 2 Live parts and bodies
In addition to reliable electrical isolation of live parts in any types of circuits from live parts in power circuits,
insulation paths shall be dimensioned for the following criteria.
Between live parts and bodies, the insulation paths of equipment for road traffic signal systems in an
enclosure (cabinet) in accordance with 5.1.1.4 shall be dimensioned for overvoltage category II and degree of
soiling 2.
NOTE Overvoltage category II: It should be assured that no overvoltage ≥ 2 500 V can be applied, otherwise protection measures are
necessary.
Degree of soiling 2: It should be assured that in general no conductive soiling can be applied (EN 60664-1/VDE 0110-1).
5.1.5.3.3 Live parts
Insulation paths between live parts of equipment for road traffic signal systems in an enclosure (cabinet) in
accordance with 5.1.1.4 shall be dimensioned.
All terminals and other connection elements for incoming and outgoing cables or wires whose operating
voltage is in excess of the extra-low voltage range shall be dimensioned in accordance with overvoltage
category III and degree of soiling 3 (e.g. the output connector blocks in controllers, the distributors in the
poles and the connection terminals in the signal heads).
5.1.5.4 Insulated devices
On equipment with an insulating enclosure and if reinforced insulation is used, the test voltage between live
parts to bodies or to metal films mounted on the outer faces of insulating enclosures shall at least have
double the values of the rated voltage. Insulation paths between live parts and bodies shall be dimensioned
for overvoltage category III and degree of soiling 3 for the rated voltage.
When the cabinet is in accordance with IP54 and an overvoltage protection is provided the insulation paths
may be dimensioned in accordance with overvoltage category II and degree of soiling 2.
Pole distributors are considered to have reinforced insulation if the test voltage between live parts and bodies
has at least three times the value of the rated voltage and the insulation paths are dimensioned in
accordance with overvoltage category III and degree of soiling 3 for three times the rated voltage.

5.2 Traffic safety
5.2.1 General
For the present subclause concerning rules for the functional safety of Road Traffic Signal Systems the
definitions for "item" and "failure" according to IEC 60050-191 shall be applied.
Failures shall be considered at different levels of the Road Traffic Signal System. Failures considered in
EN 12675 are apparent to road users, i.e. traffic and pedestrians. In this subclause those failures of items of
the Road Traffic Signal System which may lead to the faults described in EN 12675 are considered.
This subclause defines the requirements for traffic signal safety, the testing of which is defined in Clause 6.
5.2.2 Requirements of signal intensity for safety
The signal limits for safety shall be to one of the following classes:

- 15 - EN 50556:2011
Class AF1:
The luminous intensity of the light output on axis for signals which are required for safety to be ”ON”, e.g.
Red, shall be greater than 10 cd (as specified in EN 12368).
The luminous intensity of the light output for signals which are required for safety to be ”OFF”, e.g. Green,
shall be less than 0,05 cd (as specified in EN 12368).
The signal manufacturer shall specify the signal requirements either voltage, current or alternative signalling
system to ensure that the above limits are met. The system engineer shall ensure that the controller shall
provide an action on these limits.
Class AF5:
For signals which are required for safety to be ”ON” and for which monitoring of absence is required, signals
shall be considered to be switched "ON" if the voltage on the output of the controller is greater than minimum
switch on voltage for the class of signals defined as compatible. In addition a method of confirming that the
signals are drawing power (i.e. there is something connected) shall also be provided. This may be either
monitoring of the current consumed by the signals or other similar technique. Any such technique shall
consider the environmental effects on measurements and this should be demonstrated in the technical
assessment of the technique.
For signals which are required for safety to be ”OFF” shall be considered to be switched off if the voltage on
the output of the controller is less than 20 % of the full rated output voltage.

5.2.3 Requirements for signal states
5.2.3.1 Signal states which endanger traffic shall be prevented during operation of a Road Traffic Signal
System as described in 5.2.3.4. When a system is installed and operated within the manufacturer’s specified
limits and there are no random hardware failures or systematic failures (e.g. software errors) the signals will
conform to the requirements in EN 12675 for correct operation. It is not allowed to operate a system outside
of the specified limits.
5.2.3.2 Failures shall be primarily prevented by formal measures of quality assurance in development and
manufacturing as well as by correct installation. This shall be achieved by EN ISO 9001:2008 or equivalent.
The occurrence of failures shall also be limited by use of reliable components, proper operation and
scheduled maintenance.
5.2.3.3 If a failure could lead to a signal state endangering the traffic as defined in EN 12675 a functional
independent safeguarding facility shall lead to a safe state of operation as defined in EN 12675. This
safeguarding facility shall become active within a time interval specified according to the following classes:
Class AG1: 100 ms;
Class AG2: 150 ms;
Class AG3: 200 ms;
Class AG4: 300 ms;
Class AG5: 500 ms;
Class AG7: 850 ms.
NOTE This time interval is the time from the dangerous signal occurs until this state has been removed.
5.2.3.4 To ensure that the requirements of 5.2.3.1 to 5.2.3.3 are obeyed one of the following procedures
shall be carried out:
(Each country should clearly specify their requirements as to what “signal states dangerous to traffic” are, by
defining their selection from EN 12675.)
Class X1:
Both a failure mode analysis according to 5.2.4 and functional tests according to Clause 6 shall be carried out
in accordance with signal states dangerous to traffic specified in EN 12675.
Examples of failures to be considered are given in EN 50129.
Class X2:
Functional tests according to Clause 6.
5.2.4 is not mandatory.
5.2.3.5 The signal safeguarding facility shall always be active as long as the controller is powered.
5.2.3.6 The controller software consists of:
– operating system;
– application software;
– traffic safety data;
– traffic non safety data.
It shall not be possible to alter or modify the operating system or the application program of the controller, but
the software may be replaced by alternative software which has been tested and approved by the design
authority.
It shall not be possible to modify the controller traffic safety data except by an authorised event.
NOTE The modification of traffic safety relevant data by use of a handset or by data received from an external source may in certain
circumstances be classed as being authorised.
The modification of traffic non safety relevant data has no restrictions.

5.2.4 Failure consideration (Failure mode analysis)
5.2.4.1 General
The failure consideration shall be carried out according to the following rules. For information purposes these
rules are additionally depicted in Figure 1.
The consideration of failures shall be done starting from the highest hierarchical level in the system and
proceeding towards the lowest level. At each level the assessment shall be carried out until at the considered
level, all possible failures of the involved items fulfil the failure consideration. At that point the analysis shall
be considered to have been successful and the analysis shall end.
5.2.4.2 First Single Failure (Failure A)
5.2.4.2.1 The term "single failure" covers the initial failure and any further failures caused as the result of
this failure. A signal state endangering traffic (according to EN 12675) due to a "single failure" shall be
prevented.
5.2.4.2.2 If this failure could lead to a signal state endangering traffic, a functional independent
safeguarding facility shall become active within a time interval specified in 5.2.3.3. This activity of the
safeguarding facility shall initiate the failure mode as defined in EN 12675.
5.2.4.2.3 If this failure does not lead to a signal state endangering traffic, it may become apparent by an on-
line safety diagnostic check or by a scheduled manual proof test. Alternatively it may not become apparent,
see 5.2.4.3.
When the failure is detected by an on-line safety diagnostic check, it shall be disclosed within the safety
diagnostic check interval (SDCI) by stored message and it may in addition initiate an action. The action may
be a restriction of some controller functions or may initiate the failure mode.
When the failure is detected by a scheduled manual proof test, the detection shall occur within a proof test
interval (PTI) specified by the manufacturer.
The detected failure shall be repaired within an interval specified by the manufacturer.
The above mentioned intervals shall be determined in a way, that the probability of a second failure which
-5
could cause an unsafe condition occurring within those intervals is less than 10 /year, i.e. the occurrence of
a second failure shall not be expected during those intervals.
5.2.4.3 Second Single Failure (Failure B)
5.2.4.3.1 If a first "single failure" is not apparent as defined in 5.2.4.2.3, the occurrence of an additional
independent "single failure" shall be considered. A signal state endangering traffic due to the combination of
both failures shall be prevented.
5.2.4.3.2 If the combination of two independent single failures could lead to a signal state endangering
traffic a functional independent safeguarding facility shall become active within a time interval specified in
5.2.3.3. This activity of the safeguarding facility shall initiate the failure mode as defined in EN 12675.

- 17 - EN 50556:2011
5.2.4.3.3 If the combination of the two single failures does not lead to a signal state endangering traffic, it
shall become apparent by an on-line safety diagnostic check or by a scheduled manual proof test. If this is
not possible it is acceptable that the two faults remain and additional faults are considered otherwise the
design shall be considered as unacceptable.
When the failure combination is detected by an on-line safety diagnostic check, it shall be disclosed within the
safety diagnostic check interval (SDCI) by stored message and it may in addition initiate an action. The action
may be a restriction of some controller functions or may initiate the failure mode.
When the failure combination is detected by a scheduled manual proof test, the detection shall occur within a
proof test interval (PTI) specified by the manufacturer.
The detected failure combination shall be repaired within an interval specified by the manufacturer.
The above mentioned intervals shall be deter
...