Safety, Operational, and Energy Impacts of In-vehicle Adaptive Stop Displays Using Connected Vehicle Technology
The objective of this study was to assess perceived benefits of an adaptive in-vehicle stop display and to determine any negative safety implications with the use of this system. For the study, Virginia Tech Transportation Institute (VTTI) recruited 49 participants from targeted high-risk age ranges (18-25 and 55+) to drive an instrumented vehicle on the Virginia Smart Road near Blacksburg, Virginia under varying traffic and sign conditions.
For the test track experiment, the in-vehicle adaptive display system utilized a five-inch LCD monitor, positioned so it was slightly offset from the vehicle’s steering wheel and plugged in the heating, ventilation, and air conditioning (HVAC) system. Displays included the standard R1-1 stop sign, as well as an experimental sign, which informed the drivers to proceed through the intersection with caution (see image below). An auditory alert accompanied the visual displays.
Figure 1: The "Stop" and "Proceed with Caution" displays shown to the drivers during the driving test
All participants completed a series of 21 uniquely crafted scenarios. These maneuvers were designed to imitate situations one may experience in the real world while using this technology, including interactions with varying levels of traffic and equipment malfunctions or failures. The lead researcher gave the following instructions to participants prior to every scenario:
- Proceed toward the intersection at about 35 mph.
- Follow the onscreen prompt.
- Follow the lead researcher’s navigational instructions after passing through the intersection.
In this study, the change in display and associated auditory alert was triggered by the driver crossing a geo-specific threshold and activating a pre-determined sign state. However, in real world application the state of the sign will adapt based on traffic conditions using a dedicated short range communication (DSRC) network and additional connected vehicle systems.
An onboard data acquisition system (DAS) recorded all relevant kinematic and driver performance data for subsequent analysis. Data from the 100-Car Naturalistic Driving Study was used as the baseline measurement for driver stopping behaviors at stop-controlled intersections. Additional analysis determined the associated cost per user and cumulative delay incurred at traditional stop-controlled intersections when compared to an intersection in a connected vehicle environment where an adaptive stop display could be used.
- The adaptive stop display had a full compliance level of 62.11 percent while traditional stop signs had a full compliance level of 12.44 percent.
- The rate for full violations (crossing the stop bar at a speed greater than 10 mph was 1.17 percent for the adaptive stop display and 39.67 percent for traditional stop signs.
- When presented with the Proceed with Caution (PWC) display, participants exhibited more risk-averse behaviors that were appropriate when responding to situational changes that required higher levels of attention, such as an increase in traffic.
Figure 2: User cost of delay by hour
Figure 3: Delay induced daily fuel consumption
**The graphs assume a model of a rural major collector at junction with another major rural collector with an annual average daily traffic (AADT) of 1,950 vehicles.