Low-speed collisions between tractor-semitrailers and passenger vehicles may result in large areas of visible damage to the passenger vehicle, but often produce limited damage to the tractor-semitrailer. Despite this, such accidents may lead to assertions of serious injury to the tractor driver and/or sleeper compartment occupant. Research regarding the impact environment and resulting injury potential of the occupants during these types of impacts is limited. This research investigated driver and sleeper compartment occupant responses to relatively low-speed and low-acceleration impact events. Five crash tests involving impact between a tractor-semitrailer and a passenger car were conducted. The test vehicles were a van semitrailer pulled by a tractor and three identical mid-sized sedans. The occupants of the tractor included a human driver and an un-instrumented Hybrid III 50th-percentile-male anthropomorphic test device (ATD). The human driver was seated in the driver seat, restrained by the available three-point seat belt assembly, and equipped with a six-degree-of-freedom head-mounted sensor package (rotational rate sensors and accelerometers) to measure head triaxial linear accelerations and angular velocities. The ATD was equipped with a sit-stand pelvis and positioned supine and unrestrained on the sleeper cab bunk. The tractor was instrumented with accelerometers, a yaw rate sensor, and a velocity sensor, and was equipped with onboard real-time cameras to capture the driver and passenger kinematics. The tests included four sideswipe events involving extended contact between the semitrailer bottom rail and dual wheels and the sides of the sedans, and a single perpendicular collision between the semitrailer dual wheel and the right front corner of a sedan. Tractor driver head center-of-gravity (CG) linear and angular accelerations, head angular velocities, and neck forces and moments were computed. Head and neck data were compared to volunteer studies of vigorous activities of daily living, published human tolerance levels, and Injury Assessment Reference Values (IARVs) used in compliance testing of passenger vehicles. It was determined that the biomechanical responses in the head and upper neck of the driver were well below the established IARVs; and the biomechanical responses in the head, upper neck, and lower neck were lower than or comparable to the responses of these body regions to the loads experienced by volunteers during non-injurious activities. Video documentation of the kinematics of the sleeper compartment occupant was obtained. That occupant was found to remain within the sleeping compartment under all conditions and did not experience motion likely to lead to injurious contact.