2020年の開業に向けて、JR東日本が東京の山手線の品川駅と田町駅の間で建設を進めている新しい駅の工事現場が、初めて報道関係者に公開されました。
The construction site of a new station, that JR are progressing between the Yamanote and Tamachi stations with the aim of a 2020 completion, was opened to the press for the first time.
I'm struggling with the part in bold. If I'm parsing this correctly then the simplified relative clause will be
JR東日本が建設を進めている駅
My problem is that 進める already has a subject (JR東日本) and an object (建設), but I thought 駅 would be the object.
My only guess is that を isn't the object marker here but means 'through' (like the use with 歩く for example). So the clause would read 'the station that JR are progressing through the construction phase.
Am I correct or have I made a serious parsing error?