As　the　design　basis　of　the　tunnel　lighting　system,　tunnel　access　zone　luminance　(TAZL)　directly　affects　the　energy　efficiency　of　the　tunnel　lighting　system　and　the　driving　safety　of　drivers.　Affected　by　the　relative　position　of　the　sun,　weather　conditions　and　other　factors,　the　TAZL　dynamically　changes　over　time,　but　the　existing　tunnel　mostly　uses　a　fixed　luminance　value　for　the　design　and　operation　of　the　tunnel　lighting　system,　which　lacks　a　simplified　method　to　obtain　the　real-time　luminance.　In　this　study,　the　L-20(S)　(the　average　luminance　observed　by　the　driver　at　20　degrees　field　of　view)　at　the　tunnel　stopping　sight　distance　is　split,　and　the　sky　luminance　is　calculated　by　using　the　sky　luminance　model.　While　a　segmented　prediction　model　of　the　ground　scenery　luminance　is　established　with　the　maximum　sun　height　angle　as　the　inflection　point,　the　solar　irradiance　outside　the　tunnel　is　adopted　as　the　input　parameter.　This　new　proposed　L-20(S)　evaluation　model　is　verified　within　the　error　of　5.41%,　which　provides　a　convenient　and　accurate　method　for　the　real-time　measurement　of　TAZL.