DENM

DENM stands for Decentralized Environmental Notification Message, a standardized message type in cooperative intelligent transport systems (C-ITS) used to inform nearby road users about observed or imminent hazards and environmental conditions. It is defined within ETSI specifications for ITS-G5 and C-V2X communications and is designed to be broadcast to vehicles and roadside units within a defined relevance area.

A DENM conveys the event type, location and time of the event, a relevance area, duration, and indicators of severity and certainty. It can include details such as affected lanes, number of involved objects, weather or road surface conditions, and other contextual data. The purpose is to enable both human drivers and automated systems to take precautionary actions, such as reducing speed or changing route.

Generation and transmission: A vehicle or roadside unit detects a hazard or condition and generates a DENM. The message is broadcast or multicast to nearby ITS stations and is valid for a specified period. Security is provided by a PKI-based framework to authenticate sources; privacy is maintained through pseudonymity.

Applications: DENMs are used for road hazards, adverse weather, construction zones, disabled vehicles, pedestrians in the roadway, and other environmental events. They complement CAM messages, which provide ongoing location awareness, by delivering event-specific information.

Interoperability and deployment: DENMs are a core component of European C-ITS deployments and are being adopted in other regions using ITS-G5 or C-V2X technologies, with ongoing efforts to harmonize data models and semantics.