DENMs

DENMs, or Decentralized Environmental Notification Messages, are standardized V2X messages used in cooperative intelligent transport systems to broadcast information about temporary environmental events and road conditions that may affect safety or mobility. They are designed for decentralized dissemination, meaning vehicles and roadside units broadcast DENMs directly to nearby road users without relying on a central server, enabling rapid awareness and response.

A DENM conveys an event description and context. Typical fields include an event type (for example accident, road obstruction, debris, weather hazard, or unusual road condition), severity, certainty or probability, a time window, and a location reference (coordinates and/or a road segment). It may also specify a relevance distance, duration, and optional descriptive information. The message aims to be concise and timely, so that nearby receivers can assess risk and take appropriate actions such as slowing down or rerouting.

DENMs are part of the ITS-G5/C-ITS standards developed by ETSI. They are designed to work alongside other cooperative messages, such as CAMs (Cooperative Awareness Messages) and SPaT/MAP, to provide a comprehensive situational picture. Security and privacy are addressed through authenticated and integrity-protected messages, often using pseudonymous certificates to balance trust with user privacy.

Common use cases include vehicle crashes, road debris, icy or flooded surfaces, poor visibility, roadworks, and wildlife crossings. By distributing timely, location-specific hazard information, DENMs support safer driving and smoother traffic flow in connected vehicle environments.