This　paper　proposes　an　online　energy　management　strategy　for　parallel　plug-in　hybrid　electric　buses　(p-PHEBs)　based　on　a　hybrid　vehicle-road　model　to　improve　fuel　economy　and　reduce　emissions.　Firstly,　models　for　the　p-PHEB　and　energy　consumption　are　formulated,　respectively.　Secondly,　a　hybrid　vehicle-road　model　is　established　by　using　automata　based　on　traffic　information　and　vehicle　motion　modes.　Then　an　online　energy　management　strategy　based　on　the　hybrid　vehicle-road　model　is　proposed　and　implemented.　Finally,　the　p-PHEB　with　the　proposed　strategy　is　simulated　under　two　standard　roads　and　a　practical　bus　line　with　different　time　periods.　Compared　with　two　kinds　of　traditional　online　strategies,　the　simulation　results　indicate　that　the　proposed　strategy　has　better　fuel　economy　and　lower　emissions.