Manufacturer-neutral, open, future-proof:
V2X communication with the PTX interface 2.0 for traffic signal priority

Standardised, open interfaces are essential for modern information systems in public transport and therefore for local digital traffic signal priority systems. With the release of the PTX interface specification 2.0 for V2X hardware, a new milestone has now been reached. The specification was developed jointly by leading manufacturers of control systems (including INIT) and on-board units (OBUs). V2X stands for “vehicle to everything”, while PTX refers to “public transport to everything”. The new specification provides a manufacturer-neutral, open communication standard for the digital exchange of data between C-ITS on-board units (V2X OBUs) and on-board computers (IBIS) as well as the respective infrastructure, e. g. traffic signals. It therefore creates the foundation for integrating C-ITS functions into public transport vehicles.

At a time when analogue radio frequencies are increasingly being replaced by digital technologies – often requiring analogue radio equipment to be replaced – such a standard represents an important contribution to the digitalisation of public transport operations. As a result, many public transport operators are already choosing to invest in modern vehicle-to-everything technologies. V2X is not limited to public transport or emergency services: private vehicles can also communicate with one another and with urban infrastructure, enabling the exchange of relevant data. 

On buses (as shown here) or trams, the traffic light is about to turn green thanks to communication between the EVENDc on-board computer, OBU and roadside unit via V2X. (© INIT | Ulrike Kabel)

The new specification ensures reliable interoperability between on-board computers (such as INIT’s COPILOTpc and EVENDpc product lines) and V2X OBUs. This allows vehicles, for example, to communicate digitally via air interface with roadside units of traffic signal systems in order to request priority at intersections or benefit from a coordinated ‘green wave’. Time-to-green information is also supported, enabling the remaining time until a traffic light changes from red to green to be displayed. The on-board computers remain responsible for vehicle localization and the ITCS connection.

The specification defines the messages exchanged between OBU and IBIS via MQTT and provides the necessary technical foundation in the form of JSON schemas for standardization, validation and integration of the data. By introducing a uniform interface, the need for costly, proprietary infrastructure solutions is eliminated.