Nowadays,　speed-change　lane　of　freeway　interchange　is　a　big　safety　risks　area.　The　reasonable　length　of　speed-change　lane　can　effectively　reduce　the　safety　risk.　From　the　point　of　driver＇s　safety　and　comfort,　this　paper　studies　on　the　length　of　speed-change　lane　by　doing　experiment　on　drivers　driving　on　behalf　of　cars　and　trucks.　Through　the　theoretical　and　experimental　analysis,　we　study　on　vehicle　speed　and　variation　of　driver　driving　workload,　establishing　the　relationship　between　length　and　driver＇s　safety　and　comfort.　Under　the　conditions　of　the　design　speed　of　120km/h,　the　general　values　and　limit　values　of　length　which　meet　the　driver＇s　expectation　are　provided.　They　are　compared　with　the　current　specification　index　in　China.　This　paper　puts　forward　a　new　idea　and　method　to　study　on　the　length　design　index　standard　of　speed-change　lane　in　freeway　trumpet　interchange.　©　(2013)　Trans　Tech　Publications,　Switzerland.