This　paper　presents　a　study　on　the　development　of　safety　performance　function　for　freeways.　Applying　well-established　statistical　methods,　we　evaluated　all　variables　that　may　affect　freeway　safety　and　selected　the　most　significant　ones　in　the　model.　A　variable　analysis　unit　was　utilized　in　this　study　to　overcome　the　difficulties　in　obtaining　accurate　crash　and　highway　attribute　data,　as　well　as　to　improve　the　modelling　quality.　The　results　of　this　study　provide　much　needed　tools　for　freeway　safety　analysis.