Firstly,　experiments　are　conducted　on　108　sections　of　3　typical　two-lane　highways　and　the　continuous　speed　of　cars　for　experiments　are　obtained.　Then　the　speed　features　are　studied　in　these　processes,　and　the　conclusion　is　drawn　that　the　original　speed　and　the　transverse　space　between　car　and　the　roadside　intruders　are　the　primary　factors　influencing　a　car　when　it　passes　through.　The　models　of　the　impact　on　the　speed　are　also　built　using　regression　analysis.　On　this　condition,　roadside　interference　coefficients　were　put　forward　based　on　the　theoretic　analysis　of　the　relations　between　the　number　of　roadside　interferences　and　operating　speed.　Finally,　this　paper　offers　a　calculated　table　of　the　roadside　interference　coefficient　of　every　kind　of　transect　and　varied　number　of　roadside　interferences.