This　paper　studies　the　state　estimation　problem　for　a　class　of　coupled　linear　ODE-hyperbolic　PDE　systems　with　unknown　in-domain　parameters.　Based　on　the　swapping　transformation　and　the　least　squares　parameter　estimation　method,　a　Luenberger-type　adaptive　boundary　observer　is　designed　to　estimate　the　ODE-PDE　states　under　the　unknown　parameters.　The　exponential　convergence　conditions　w.r.t.　the　observer　feedback　gains　are　given　by　employing　the　Lyapunov　technique.　Finally,　an　application　to　traffic　state　estimation　of　the　Aw-Rascle-Zhang　(ARZ)　model　involving　the　unknown　relaxation　time　and　the　boundary　input　speed　deviation　is　provided　to　validate　the　theoretical　result.　(c)　2024　Elsevier　Ltd.　All　rights　are　reserved,　including　those　for　text　and　data　mining,　AI　training,　and　similar　technologies.