Naturalistic Passenger Behavior: Posture and Activities

Abstract

Video cameras were installed in the passenger cabins of 75 vehicles to monitor the postures and activities of front-seat passengers. Video frames from a total of 2733 trips were coded for 306 unique front-seat passengers. During these trips, a total of 13638 frames were coded; each frame represents about four minutes of travel time. The median trip duration was 12.2 minutes and 5% of trips were longer than 54 minutes. The distribution of trip durations was similar to that for the general population of US travelers. The front seat passenger was female in 72% of frames and most often judged to be between 17 and 30 years of age. The seat belt was worn 97% of the time, with visibly poor fit (belt on belly or lateral to the clavicle) in about 30% of frames. The most common passenger interaction was talking with the driver, while interactions with hand-held devices (typically phones) occurred in 26% of frames. Phone use was associated with a downward pitched head. The head was rotated left or right in 33% of frames, and the torso was rotated left or right about 10% of the time and pitched forward in almost 10% of frames. The front of the thighs was lifted off the seat due to the feet being shifted rearward about 40% of the time and the legs were crossed in about 5% of frames. Resting behavior was observed more frequently in longer-duration trips and when traveling at higher speeds, while phone use increased and talking with vehicle occupants decreased with increased sitting time. No seat position or seat back angle change was noted in 40 (53%) of vehicles. In the remaining 35 vehicles, seat back angle and seat position were observed to change only 16 and 61 times, respectively, so that the distributions of seat position and seat back angle on arrival were essentially unchanged during travel. The seat was positioned full-rear on the seat track about 23% of the time and rearward of the mid-track position in 81% of frames. The mean seat back angle was 25.4 degrees (standard deviation 6.4 degrees); seat back angle was greater than 30 degrees in 15% of frames and greater than 35 degrees in less than 1% of frames. Seat back angles greater than 30 degrees were more common on longer trips and associated with a greater likelihood of the head touching the seat, lower phone use, and slightly greater frequency of resting behavior. When a second-row passenger was present behind the front-seat passenger, the seat was 5 mm further forward and 1.4 degrees more upright, on average. This study is the first to report distributions of seat positions and seat back angles for front-seat passengers and the first to provide details of passenger posture and activities from a large sample of individuals. The findings have implications for the design of current vehicles and also provide insight into the likely postures and activities of the occupants of future driverless vehicles.