Vulnerable Road Users

Description

Within the 3GPP framework for Vehicle-to-Everything (V2X) communications, Vulnerable Road Users (VRU) refers to a functional role or entity representing road users who are not inside a protected vehicle chassis and are therefore at higher risk of injury in a collision. This primarily includes pedestrians, cyclists, riders of powered two-wheelers (e.g., motorcycles, scooters), and potentially also wheelchair users or horse riders. 3GPP specifications, particularly from Release 14 onwards, define service requirements and technical architectures to facilitate V2X applications aimed at protecting VRUs. The core idea is to integrate VRU devices (typically smartphones, dedicated wearables, or sensors on bicycles) into the V2X ecosystem, allowing them to broadcast their presence and receive warnings from vehicles and infrastructure.

The technical operation involves two main communication interfaces defined for V2X: the Uu interface (through the cellular network) and the PC5 interface (direct device-to-device communication, also known as sidelink). A VRU device can use either or both. Using PC5, a VRU device can periodically broadcast its basic safety message (e.g., a VRU Awareness Message) containing its position, speed, heading, and type (e.g., pedestrian). Vehicles equipped with V2X capabilities receive these messages via their own PC5 interfaces. The vehicle's onboard application can then assess the collision risk and provide a warning to the driver or initiate automated braking. Conversely, a vehicle can broadcast warnings (e.g., about a hard brake) that VRU devices can receive and convert into an audible or haptic alert for the pedestrian or cyclist.

When using the Uu interface, the VRU device's location and status can be reported to a V2X application server in the network (using the Service Enabler Architecture Layer for Verticals - SEAL). The server can perform broader area analytics, detect hazardous situations involving multiple entities, and disseminate targeted warnings back to relevant vehicles and VRUs through cellular broadcast or unicast. This network-assisted approach allows for longer-range hazard awareness and scenarios where direct PC5 communication might be limited by range or obstruction. The 3GPP architecture defines the necessary service requirements, message structures, and functional procedures to support these VRU safety applications, ensuring interoperability between devices from different manufacturers and vehicle OEMs.

Purpose & Motivation

The formalization of VRU support in 3GPP standards was motivated by the global road safety challenge. Traditional vehicle-centric safety systems (like airbags, crumple zones) do not protect people outside the vehicle. As V2X technology evolved to enable vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communication for automotive safety, a significant gap remained: the inclusion of the most vulnerable participants in traffic. The primary problem addressed is the detection and awareness of VRUs in complex urban environments, especially in non-line-of-sight or occluded scenarios where a vehicle's onboard sensors (cameras, radar) may fail.

3GPP-based V2X communication provides a complementary sensor with longer range and the ability to 'see around corners' via network relay. By bringing smartphones—nearly ubiquitous devices carried by pedestrians and cyclists—into the safety system, 3GPP standards create a scalable path to dramatically improve VRU safety. The work, initiated in Release 14 and enhanced in later releases, was driven by use cases defined by automotive standards bodies like ETSI and the desire to create a comprehensive, cellular-integrated Cooperative Intelligent Transport Systems (C-ITS) ecosystem. It addresses the limitations of previous, non-cellular dedicated short-range communication (DSRC) proposals by leveraging existing cellular device penetration and the network's ability to manage identities, security, and wide-area services.