  The use of real-time software-controlled reconfigurable intelligent surface
(RIS) units is proposed to increase the reliability of vehicle-to-everything
(V2X) communications. The optimum placement problem of the RIS units is
formulated by considering their sizes and operating modes. The solution of the
problem is given, where it is shown that the placement of the RIS depends on
the locations of the transmitter and the receiver. The proposed RIS-supported
highway deployment can combat the high path loss experienced by the use of
higher frequency bands, including the millimeter-wave and the terahertz bands,
that are expected to be used in the next-generation wireless networks, enabling
the use of the existing base station deployment plans to remain operational,
while providing reliable and energy-efficient connectivity for autonomous
vehicles.
