Field Study Found Adaptive Cruise Control Reduced Speed Fluctuations by 59 Percent and Increased Average Speed by Up to 2.2 mph Compared to Conventional Vehicles.
Participants Driving on a Test Track in Virginia Were Monitored to Understand the Effects of Automated Driving.
Thornburg
Exploring the Effects of Vehicle Automation and Cooperative Messaging on Mixed Fleet Eco-Drive Interactions
Summary Information
The gradual introduction of infrastructure and automated vehicle can result in vehicles equipped with varying levels of cooperative driving automation (CDA) while sharing the road with conventional vehicles. These interactions may confuse drivers and lead to unpredictable behaviors, particularly if automated vehicles operate based on information that is only available through CDA systems.
This field study explored human driver behavior and perspectives when following a simulated Level 3 advanced CDA vehicle to a signalized intersection. It aimed to assess whether speed fluctuation and following distance differed between drivers using adaptive cruise control (ACC) and drivers not using ACC, as well as their stopping and acceleration/deceleration patterns at signalized intersections.
METHODOLOGY
Eighty participants from the area of Thornburg, Virginia, drove a test vehicle nine loops around a test track where each loop consisted of two trials through a traffic signal. The test track was a closed-course racetrack in Virginia. Half the participants drove an ACC-enabled vehicle and half drove a conventional vehicle. They received one of four message conditions (i) no messages, (ii) signal status message, (iii) lead vehicle intent message, and (iv) signal status and lead vehicle intent message, via a smartphone mounted on the dashboard. During each loop, participants followed a lead vehicle while approaching a traffic signal with five signal scenarios. The vehicles were equipped with cameras and sensors for researchers to monitor in real-time. After completing each loop, participants answered mid-drive questions. After nine loops, participants completed a post-experiment questionnaire.
FINDINGS
- Participants in ACC vehicles had 59 percent fewer total speed fluctuations than participants in conventional vehicles (50 versus 121).
- Participants in ACC vehicles had higher average speeds (0.1 to 2.2 mph greater) and smaller speed variability (0.1 to 1.1 mph less) than the participants in conventional vehicles.
- Participants in conventional vehicles tended to apply the brakes more often (1.5 to 5.4 percent) than participants with the same message types in ACC vehicles.
- Participants in conventional vehicles who received CDA messages had shorter following distances (0.1 to 0.4 s) than those who did not receive CDA messages; however, this difference was not always significant.
- Across all scenarios, participants in ACC vehicles had shorter following distances than participants with conventional vehicles (0.1 to 1.1 s shorter).
- Participants in conventional vehicles ran the red light between 6 and 20 percent, whereas the participants in ACC vehicles ran the red light about 40 to 75 percent of the time. The reason for this outcome was unclear.
- Participants reported relatively high trust in the lead automated vehicle regardless of whether the drivers were receiving CDA messages.
