Median　openings　are　an　effective　traffic　organization　mode　for　freeway　crossover　work　zones,　and　their　length　is　one　of　the　most　important　control　indicators　to　ensure　traffic　safety　in　work　zones.　In　this　paper,　a　theoretical　calculation　model　of　the　median　opening　length　was　established　according　to　the　lane-changing　demands　of　vehicles　crossing　through　the　median　opening　of　the　freeway.　Based　on　the　calculation　model,　the　influencing　factors　of　the　median　opening　length　were　analyzed,　and　the　calculation　values　of　the　median　opening　length　under　different　speed　limits,　median　widths　and　cross　slopes　were　proposed.　A　naturalistic　driving　experiment　of　drivers＇　safety　and　comfort,　with　48　participants　at　four　opening　lengths　of　40,　70,　100　and　130　m　in　a　typical　freeway　work　zone,　was　carried　out　based　on　the　calculated　length　values　and　the　driving　workload,　expressing　drivers＇　safety　and　comfort.　It　was　found　that　the　median　opening　length　of　the　freeway　had　a　positive　correlation　with　the　vehicles＇　running　speed　and　the　drivers＇　driving　workload:　the　shorter　length　reduced　the　running　speed　of　the　vehicles　and　led　to　uncoordinated　running　speeds　in　the　work　zone;　the　longer　length　caused　driver　tension　and　led　to　the　vehicles＇　running　speed　and　speed　variability　being　too　high.　The　research　results　indicated　that　the　median　opening　length　of　freeway　work　zones　is　an　important　factor　affecting　the　vehicle　running　speed,　driving　workload　and　speed　limit　compliance　rate.