Semi-autonomous systems represent an intersection between human control and machine assistance. When contrasted against fully autonomous systems the differentiating factor is the level of direct human control in the system during operation. Semi-autonomous systems can leverage human judgement in unexpected situations whereas fully autonomous systems must rely on their programming to handle all scenarios.

flowchart LR
    subgraph CCC ["` `"]
        UE@{ shape: trap-t, label: "Unexpected event in unpredictable environment" }
        UE --> DMSR
    end
    subgraph DMSR[Decision maker - system relationship]
        H[Human operator]
        M[Machine]
        C[Automated]
        D[Semi-Autonomous]
        E[Autonomous]

        H --> C
        H --> D
        M --> D
        M --> E
    end
    classDef container fill:none,stroke:none,color:none;
    classDef dmsr fill:none,stroke:black;
    classDef human fill:#66050560,stroke:black,color:black;
    classDef machine fill:#00336660,stroke:black,color:black;
    classDef automated fill:#37373760,stroke:black,color:black;
    classDef semiauto fill:#15711560,stroke:black,color:black;
    classDef autonomous fill:#80500060,stroke:black,color:black;
    classDef decison_maker fill:transparent,stroke: transparent;
    class H human
    class M machine
    class C automated
    class D semiauto
    class E autonomous
    class DM decison_maker
    class DMSR dmsr
    class UE ue
    class CCC container
    linkStyle 0 fill:none,stroke:none;

Semi-autonomous systems in the real world

  1. Advanced driver-assistance systems (ADAS) enhance safety and driving ease but they don’t entirely replace the driver yet.

  2. Train systems

  3. Maritime vessels (MASS)

  4. Medical/assistive robots

  5. Robotic vehicles in defence / logistics


Semi-autonomous systems are more independent and agile than automated systems and less self-contained than fully autonomous systems. Note that even fully autonomous systems must have some kind of monitoring and direct human control in case of an emergency or if the system becomes rogue; the human user is typically not involved in an autonomous system unless it is actually necessary, unlike the shared system control between the computer and the human user in a semi-autonomous system.

There is some overlap here because a standard definition hasn’t been created, a standard set of terminology is sorely needed.