A Survey on LoRa-Based Multi-Hop Communication Systems for Vehicular Accident Detection and Emergency Response

—Road traffic accidents continue to be a major public safety concern, where the chances of survival depend heavily on how quickly emergency services are notified and deployed. Existing accident alert systems that rely on GSM or LTE connectivity often fail in remote and highway environments due to weak or inconsistent network coverage, leading to delayed rescue response. LoRa, a low-power wide-area communication technology, has emerged as a strong alternative due to its long range, low-energy transmission capabilities that operate indepen dently of cellular infrastructure. Current LoRa-based accident detection systems typically combine accelerometer-based impact sensing with GPS localization to generate emergency alerts; how ever, most implementations depend on single-hop transmission, resulting in limited communication range and reduced reliability in sparse vehicular environments. Recent studies have explored multi-hop LoRa communication, where vehicles or roadside modules relay messages over multiple nodes to extend network reach and improve alert delivery. While these approaches offer improved scalability and robustness, challenges remain in routing optimization, mobility handling, packet collision reduction, and temporal synchronization. This paper reviews existing single-hop and multi-hop LoRa-based vehicular accident alert architectures, evaluates their strengths and limitations, and outlines future research directions toward adaptive routing, hybrid LoRa–cloud coordination, and resilient communication frameworks for real world intelligent transportation systems.