In this article, we explore the recent Third Generation Partnership Project (3GPP) long-term evolution (LTE) device-to-device (D2D) radio resource management specification (Release 14) to identify the challenges and evaluate the potential of unsupervised LTE D2D (mode 2) for safety-critical vehicle-to-everything (V2X) communications. We also propose two distributed resource allocation strategies for unlicensed band access. Complementary to dedicated short-range communication (DSRC)/intelligent transport system (ITS)-G5, unsupervised LTE D2D presents an opportunity to provide redundancy for ultrareliable systems, such as safety-critical V2X communications.