Douglas Young

Preferred time-headway of highway drivers

The preferred time-headway of drivers in highway conditions is related to the likelihood of rear-end collisions. We studied traffic data from a section of southbound highway 101- a heavily commuted eight-lane freeway between San Francisco and the Silicon valley in California. We observed two parameters that drivers regulate during free flow, rush hour, and heavy traffic conditions: (1) the speed of their vehicle; and (2) the time-headway to the preceding vehicle. During free flow traffic, the preferred speeds show low variation within lanes, but large variations from lane to lane. During rush hour traffic, the time-headway between vehicles varies between 1 and 2 s for a range of traffic speeds. For all traffic conditions a lower limit of 1s is seen in time-headway, even when traffic volume does not push drivers toward tight spacing. The lower limit of 1s is consistent with what was found in several previous studies, but is significantly shorter than the 3s headway that is recommended by driving manuals. The short time-headways observed are within the limit of typical reaction time for braking by alert drivers, but probably lead to occasional accidents given variability in reaction times, decisions, and vehicle braking capabilities, especially when preview information is not available.

Driver Distraction and Advanced Vehicle Assistive Systems (ADAS): Investigating Effects on Driver Behavior

The component technologies of Advanced Driver Assistive Systems (ADAS) are becoming increasingly automated, with systems capable of operating in concert in multiple driving environments. However, how these systems affect a driver’s ability to safely, efficiently, and comfortably operate a vehicle remains unclear. We investigated the effects of ADAS [specifically Lane Departure Warning (LDW)] on driving performance while participants performed a secondary task (mental math) designed to simulate cognitive effort while driving. The experiment was conducted on a closed-course test track in an instrumented vehicle. Results suggest that cognitive engagement influenced driver control of the vehicle. Effects of cognitive engagement in a secondary task were not mitigated by the presence of LDW. We discuss our results in the framework of a continued need for active input and control from the human operator in vehicles with assistive technologies.

Efficacy and Usage Patterns for Three Types of Rearview Camera Displays During Backing Up

The usage of rearview camera displays and their effectiveness on drivers’ capability to avoid unexpected obstacles during four common backing tasks (i.e., parallel parking, backing between two vehicles, backing down a driveway, backing out of a garage) was evaluated on a closed-course with stationary confederate vehicles, signage, and lane markings. The obstacle consisted of either a stationary or a moving target that appeared to the rear of the test vehicle. Eye movements and vehicle dynamics measurements (i.e., longitudinal acceleration, brake displacement) were recorded, in addition to obstacle hit/avoidance rates. Performance was assessed for four rearview camera (RVC) conditions: small center-stack display (SD), large center-stack display (i.e., navigation screen) (LD), in-mirror display (IMD), and no display (ND). Test participants comprised drivers of both sexes between the ages of 18 and 68 who reported having no experience with rearview camera displays in their current or previously owned vehicles. The results showed that having an RVC display dramatically improved obstacle avoidance rates under the conditions tested. Higher avoidance rates were documented when the IMD or SD was available compared to the LD. Not all drivers relied upon RVC displays, however, even when these were available to them. Usage rates were lowest for the large center-stack display and highest for the IMD. Eye movement data indicate that drivers spent a higher proportion of time during backing tasks looking at the IMD compared to the other two displays without severe decreases in the duration of time spent looking at the rearview and side mirrors. Thus, under certain backing conditions, RVC displays, and the IMD in particular, have the potential to aid drivers in detecting and avoiding collisions while being used in conjunction with other sources of visual information (e.g., rearview and side mirrors).

Differing Perceptions of Advanced Driver Assistance Systems (ADAS)

The extent to which drivers’ attitudes toward the use of autonomous vehicle systems can be influenced by various driver factors (e.g., driver age, experience with the systems, etc.) has yet to be firmly established. To investigate driver perceptions and acceptance of advanced vehicle systems, the current research examined initial and repeated exposure to systems while driving under various commonly encountered on-road situations (e.g., emergency braking). Somewhat surprisingly, driver perceptions of safety when driving vehicles with assistive technologies diminished following repeated exposure to the technologies. However, when drivers were afforded more extensive experience, they reported a heightened appreciation of the systems—especially drivers who might benefit most from this assistance (e.g., distracted or older drivers).

Gaze behavior during curb approach: The effect of mobile device use while walking

Mobile device use is becoming increasingly prevalent during everyday activities. The simultaneous use of such technology while performing various activities may increase risk of human error and accidents, such as falls. In addition to effects on cognitive and attentional resources, mobile device use may influence visual behavior, thus affecting the user’s ability to perceive obstacles in the environment and respond appropriately. The purpose of this study was to examine the influence of texting on gaze behavior during the approach and negotiation of a simulated curb. Wireless eye-tracking was used to record gaze during locomotion, with and without concurrent texting. Semantic Gaze Mapping (SMI, Inc.) was used to co-register participants’ gaze to different areas of interest (AOIs). Texting resulted in significant reductions in gaze dwell time on the curb and the number of times the curb was fixated. These findings suggest that mobile device use may have a negative effect on navigation during locomotion by reducing visual attention to task-relevant areas along the future path of travel.

Passenger Seat Belt Usage Rates on Shuttle Buses

The National Highway Traffic Safety Administration (NHTSA) recently published a final rule requiring lap/shoulder seat belts in all new large motorcoaches and buses manufactured on or after November 28, 2016 (NHTSA, 2013). Studies of vehicle belt use in passenger vehicles demonstrate that many factors other than availability influence whether a seat belt is used by an individual in a particular circumstance. The present observational study examined passenger seat belt use in airport shuttle buses traveling short distances over urban roads with frequent stops, in four U.S. cities. Seat belts were used very rarely when provided - only 1% (2 out of 156) of passengers buckled up. These findings are consistent with other studies of passenger seat belt use in motorcoach buses, and suggest that without concomitant legislation mandating and enforcing seat belt usage, the vast majority of bus passengers are unlikely to use seat belts even when provided.