discussion only the track mechanisms associated with the forward center door leaf 16b is shown and its operation described it should be understood however that what is true concerning the track mechanisms of the door leaf 16b is also true of the track mechanisms associated with the door leaf 16a the two upper track mechanisms 18 share a common well 24 likewise the two lower track mechanisms 22 share a common well 26 the wells are conveniently located near the respective upper and lower edges of the opening 14 the wells are preferably formed as enclosures within the car profile the middle track mechanism of each door leaf is located partly in its own well 28 and 30 the remaining part of the track mechanism is mounted directly to the door leaf as is common with plugged doors a rubber seal not shown is fitted around the door leaf edge to provide a weather seal in addition the butt edges leading edges 32 and 34 of the door leaves 16b and 16a respectively comprise pressure sensitive edges which will cause the door to open if an obstruction is between them such sensitive edges are known see for example u s pat no 3 133 167 in fig2 the relative positions of the elements of the upper first track mechanism 18 are shown for a closed and plugged door condition as noted above only the upper track mechanism 18 of the door leaf 16b is shown note that the front surfaces 1b 39 and 10 39 of the door leaf and vehicle body respectively are flush in the plugged condition note also that in the region of the door leaf vehicle.