Enhanced Safety Messages (ESM): A Practical Alternative to V2X Basic Safety Messages

A very important use case of V2X communications is the enhancement of roadway safety by utilizing the transmission of road information among vehicles. The SAE Basic Safety Message (BSM) is the most common standard used to transmit road event information and their locations based on global latitudinal and longitudinal coordinates of transmitting vehicles. In practice, however, global coordinate estimations are inherently limited by the accuracy of Global Navigation Satellite Systems (GNSS) such as GPS. GNSS signals can also be unavailable in urban canyons and tunnels, be spoofed to force incorrect localization, or be restricted to low accuracy due to the sparsity of available groundbased corrections (such as RTK base stations) in rural and remote areas. In this paper, we introduce Enhanced Safety Messages (ESMs), a backward-compatible BSM replacement that adopts the well-established foundations of information redundancy in safety-critical systems to avoid catastrophic failure by providing both absolute and relative coordinate frames to robustly describe vehicle locations. This position information redundancy in two different coordinate systems, one from external sources and another from local sensing, effectively addresses the BSM drawbacks of relying entirely on GNSS signals. Specifically, ESM includes LaneContext and MapContext to address two of the most common driving environments of open spaces and urban roadways. Location communication over ESM is enhanced by additionally specifying the connected vehicle's driving lane, its offset from the center of the lane, and its longitudinal position along the road segment. Our experimental evaluation confirms that ESM's inclusion of relative positioning rectifies the core BSM weaknesses in relying only on global GNSS coordinates.