B-pillar
B-pillar means the forwardmost pillar on each side of the vehicle that is, in whole or in part, rearward of a transverse vertical plane passing through the seating reference point of the driver's seat, unless:
(1) There is only one pillar rearward of that plane and it is also a rearmost pillar; or
(2) There is a door frame rearward of the A-pillar and forward of any other pillar or rearmost pillar.