Large　speed　gaps　may　increase　risks　between　adjacent　speed　zones.　Therefore,　a　speed　transition　zone　is　designed　to　provide　a　smooth　change　between　two　highway　segments　with　different　speed　limits.　The　purpose　of　this　study　is　to　establish　a　procedure　for　transitional　speed　zone　design　on　two-lane　roads　by　using　drivers＇　behavioral　statistics.　In　order　to　evaluate　the　effect　of　the　speed　limit　zone　on　drivers＇　deceleration　behaviors　when　passing　different　speed　zones,　two　factors　were　considered　in　this　study:　existence　of　work　zones　and　horizon　curves.　The　speed　gaps　in　this　experiment　are　50　km/h　in　work　zone　areas　and　20　km/h　respectively.　By　using　randomly　selected　drivers,　the　study　measured　drivers＇　actions　in　a　real　vehicle　under　the　simulated　environment　traveling　between　speed　zones　at　a　0.03　second　intervals.　Several　different　measures　of　effectiveness　were　used　to　compare　the　characteristics　of　the　speed　distributions,　including　average　speed,　85th　percentile　speed　and　pace　speed.　Results　show　that　there　is　a　significant　difference　in　speed　choice　for　deceleration　between　two　scenarios　due　to　speed　reduction.　The　relationship　between　speed　limit　reduction　and　deceleration　length　is　described　by　a　linear　model.　The　length　of　the　deceleration　section　is　estimated　by　the　model.　Results　show　that　the　deceleration　section　is　positively　correlated　to　speed　reduction.　The　modeling　process　gives　detailed　guidance　for　the　design　of　a　transitional　speed　zone.　©　2010　ASCE.