The present disclosure provides vehicle collision avoidance system (CAS) that includes a first CAS module for a robotic vehicle that includes an interface to a first network; a hard stop interface communicatively coupled to the robotic vehicle; one or more computer processors; one or more computer readable storage media; and program instructions stored on the one or more computer readable storage media for execution by at least one of the one or more computer processors, the stored program instructions including instructions to: determine a relative position of a second CAS module based on information from the first network; responsive to determining that the second CAS module is within a first distance from the first CAS module, issue an alert; and responsive to determining that the second CAS module is within a second distance from the first CAS module, transmit a hard stop signal to the robotic vehicle.