A vehicle configured to operate in an autonomous driving mode, the vehicle comprising a driving unit including: a driving system including a steering subsystem , an acceleration subsystem and a deceleration subsystem to control driving of the vehicle in the autonomous driving mode; a perception system including one or more sensors configured to detect objects in an environment surrounding the vehicle based on obtained sensor data; a coupling system configured to pivotally couple to an articulating unit ; and a control system operatively connected to the driving system and the perception system, the control system having one or more computer processors configured to receive sensor data from the perception system and to direct the driving system when operating in the autonomous driving mode based on the sensor data received from the perception system; characterized by at least one of the control system and the perception system is further configured to: estimate an orientation of the articulating unit based on the obtained sensor data; and determine a pose of the articulating unit according to the estimated orientation, wherein at least one of the control system and the perception system is further configured to determine a major face of the articulating unit from the obtained sensor data, wherein the determination of the major face includes an evaluation of whether a detected surface of the articulating unit is a front surface or a side surface according to a comparison of obtained data points closest to and farthest from a given one of the one or more sensors. a driving system including a steering subsystem , an acceleration subsystem and a deceleration subsystem to control driving of the vehicle in the autonomous driving mode; a perception system including one or more sensors configured to detect objects in an environment surrounding the vehicle based on obtained sensor data; a coupling system configured to pivotally couple to an articulating unit ; and a control system operatively connected to the driving system and the perception system, the control system having one or more computer processors configured to receive sensor data from the perception system and to direct the driving system when operating in the autonomous driving mode based on the sensor data received from the perception system; characterized by at least one of the control system and the perception system is further configured to: estimate an orientation of the articulating unit based on the obtained sensor data; and determine a pose of the articulating unit according to the estimated orientation, estimate an orientation of the articulating unit based on the obtained sensor data; and determine a pose of the articulating unit according to the estimated orientation, wherein at least one of the control system and the perception system is further configured to determine a major face of the articulating unit from the obtained sensor data, wherein the determination of the major face includes an evaluation of whether a detected surface of the articulating unit is a front surface or a side surface according to a comparison of obtained data points closest to and farthest from a given one of the one or more sensors. <EOS>