Some major airport in the United States and abroad use a system called runway status lights. It is a fully automatic, advisory system used to inform pilots and ground crews if the runway is unsafe, i.e. runway crossings or an aircraft is about to takeoff or land. It is designed to prevent the possibility of runway incision incidents.
Link to FAA description of (RWSL):
https://www.faa.gov/air_traffic/technology/rwsl/
Another system that some airports are starting to implement is eFAROS, or enhanced final approach runway occupancy signal. eFAROS is a modification to PAPI approach signals that notifies approaching pilots if the runway is occupied. It works fully autonomously, scanning the runway for obstacles i.e. aircraft or vehicles. If an obstacle is detected the PAPI lights will begin flashing to notify an approaching pilot if the runway is occupied.
Link to pdf of how it works in the beta test at KBOS:
https://alpajapan.org/cp-bin/wordpress/wp-content/uploads/15SAB00730JUN14-eFAROS-evaluation-begins-at-Bostons-Logan-International-Airport-KBOS.pdf
Helpful links:
Link to FAA Runway Safety [improvement] plan:
Link to NextGen, FAA’s modernization of US airspace:
https://www.faa.gov/nextgen/