LOSS　(Level　of　Service　of　Safety)　is　used　to　weigh　the　quality　of　safe　operation　that　roads　provide　to　the　drivers　and　other　traffic　participants.　Reasonable　speed　limit　not　only　controls　the　speed　of　vehicles　in　appropriate　range　on　the　road,　but　also　guarantees　the　traffic　safety　of　the　road.　Crash　rate　was　selected　as　a　quantitative　indicator,　hierarchical　standard　of　LOSS　for　freeway　and　arterial　highway　was　studied,　and　then　the　LOSSs　of　freeway　and　arterial　highway　in　China　were　divided　into　4　levels.　In　virtue　of　the　probability　statistics,　robust　regression　and　on　the　basis　of　accident　data,　speed　limit　and　geometric　factors　the　accident　prediction　models　were　established.　Based　on　the　acceptable　LOSS　the　method　of　setting　speed　limits　about　cars　and　trucks　respectively　was　formed.　The　results　would　help　traffic　engineers　in　Chinese　highway　management　departments　choose　right　speed　limits　for　freeway　and　arterial　highway.　©　2010　ASCE.