Field Experiments in Illinois Found that Digital Alerts Increased Driver Reaction Distance by Four Times and Decreased Speed Variability by 43 Percent.
Analysis of Video Footage on I-80 and I-55 in Evaluated Driver Behavior and Compliance with Illinois’ Move Over Law.
Illinois, United States
Evaluation of Digital Alert Systems Associated with Emergency Response Vehicles and Compliance with Move Over Law
Summary Information
Crashes involving stationary roadside vehicles are a serious safety concern for police and other emergency responders. This study evaluated the impact of digital alert systems through navigation platforms, with the goal of understanding how they affected driver behavior and compliance with Illinois’ Move Over Law. The law, variations of which are in place throughout the United States, require drivers to slow down and change lanes when approaching emergency or other stopped or disabled vehicles.
METHODOLOGY
The study collected about 10 hours of high-resolution video footage with a helicopter in two major field experiments. The collected video footage was then used to extract the trajectories of all observed vehicles. The first data collection was conducted on I-80 near Kendall County, Illinois, for one afternoon in July 2024. The video recorded a roadway segment of approximately 0.5 miles, covering both upstream and downstream of a stationary police vehicle in the shoulder. Driver responses were tested in four scenarios: 1) combined digital and emergency light alerts, 2) emergency lights only, 3) no alerts, and 4) normal traffic. The second data collection effort was conducted on I-55 in Springfield, Illinois over three days in July 2025. This data collection included an additional basic freeway segment, on-ramp and off-ramp locations, and scenarios involving an Illinois Department of Transportation maintenance truck.
FINDINGS
- In the 2025 data, digital alerts increased driver reaction distance by four times (1,312 feet) compared to emergency lights alone (262 feet).
- In the 2024 data, speed variability in the outer lane dropped by 43 percent when digital alerts were active (8 mph) versus emergency lights alone (14 mph), indicating less abrupt braking.
- In the 2024 data, average number of lane changes per vehicle from the outer to inner lane were highest with the lights only scenario (0.41), followed by full alerts (0.36), no alerts (0.20), and no vehicle (0.05). The study hypothesized that this might have been because some drivers initiated lane changes before entering the video frame.
- Overall, the study concluded that digital alerts shifted both lane-changing locations and speed-reduction points upstream relative to a stationary roadside emergency vehicle.
