EN 12675 Traffic Signal Controllers - Functional Safety Requirements

The European standard “EN 12675 Traffic signal controllers - Functional safety requirements” describes the functional safety requirements for traffic signal controllers. This standard is applicable to permanent and temporary installed traffic signal control equipment and to portable traffic signal equipment that cannot control the movements of passing vehicles or pedestrians, with the exception of portable traffic signal equipment that can only control alternative/shuttle operating lanes. Traffic signal controllers defined by this standard must safely control conflicting traffic, both vehicles and pedestrians. Examples include intersection signals, pedestrian crossings, shuttle signals, public transport signals.

Electrical safety requirements and additional traffic safety requirements, interfacing with external equipment and test methods to verify compliance with this European Standard are contained in the standard “EN 50556 Road traffic signal systems”. For this standard and EN 50556 to be fully applicable, national standardization organizations are requested to define the relevant class set for their national requirements. National requirements may specify specific conditions for public transport signals and other signals not specified in a European standard.

For the purposes of this standard, the following terms and definitions apply:

• No signal refers to the signal whose light intensity does not meet the signal “on” requirements.
• A bicycle signal is a special purpose traffic signal for directing bicycle traffic in signalized areas.
• Centralized control is the system for coordinating and monitoring a traffic signal network or group using a central computer or equivalent device and transmission systems.
• Conflicting green is the simultaneous display of green signals that allow conflicting traffic movements.
• Conflicting signal groups are groups of two or more signals that, when operated simultaneously, will result in conflicting traffic movements.
• Fault mode is the inoperative state of the traffic signal controller in which the normal operating mode is replaced by a flashing amber or signal off state as a result of a major fault.
• A green signal is a signal that is displayed to traffic in green color.
• A major failure is a failure resulting in the signal traffic system not being able to operate safely as defined in national requirements.
• Manual operation mode is the operating state of the traffic signal controller in which the status of signals given to traffic is controlled manually.
• Minor faults are faults other than a major fault that are defined in national requirements and can be identified and recorded.
• Mode is the specific state of a traffic signal controller used to control traffic signals. For example, fixed-time operation mode, traffic-dependent operation mode, standby operation mode, manual operation mode, fault mode.
• Public transport signals are special purpose traffic signals for directing public transport vehicles in signalized locations.

The purpose of this European standard is to specify the functional safety requirements for equipment used for the control of traffic signals. This standard concerns the control of signals to traffic and the associated signalled traffic movements. The primary concern is to protect persons and objects from hazards arising from conflicting signals to traffic.

Hazards to consider include, but are not limited to, the following types of possible signal failures:

• Not showing red signal to traffic
• Show green signal to conflicting traffic
• Not showing the correct signal order to traffic
• Failure to ensure correct timing of all signals

Persons who need to be protected are:

• Traffic signal users, vehicle drivers and passengers (including public transport), pedestrians, cyclists and equestrians, physically disabled persons
• Maintenance and inspection personnel

Traffic signal controllers are the core part of the traffic signal control system in the city, and are the sub-execution unit of large and small intersections. Its main function is to realize intersection traffic signal control, traffic information acquisition, communication, intersection monitoring, etc. Traffic signal controllers are suitable for T-junctions, intersections, multiple forks, road sections, ramps and other traffic points. These controllers can operate a variety of different control modes and intelligently switch between control modes. As the number of transportation modes to be handled increases, traffic signal controllers become more complex.

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