Abstract--Traffic safety analysis at signalized intersections is vital for reducing vehicle and pedestrian collisions, yet traditional crash-based studies are limited by data sparsity and latency. This paper presents a novel multi-camera computer vision framework for real-time safety assessment through Post-Encroachment Time (PET) computation, demonstrated at the intersection of H Street and Broadway in Chula Vista, California. Four synchronized cameras provide continuous visual coverage, with each frame processed on NVIDIA Jetson AGX Xavier devices using YOLOv11 segmentation for vehicle detection. Detected vehicle polygons are transformed into a unified bird's-eye map using homography matrices, enabling alignment across overlapping camera views. A novel pixel-level PET algorithm measures vehicle position without reliance on fixed cells, allowing fine-grained hazard visualization via dynamic heatmaps, accurate to 3.3 sq-cm. Timestamped vehicle and PET data is stored in an SQL database for long-term monitoring. Results over various time intervals demonstrate the framework's ability to identify high-risk regions with sub-second precision and real-time throughput on edge devices, producing data for an 800 800 pixel logarithmic heatmap at an average of 2.68 FPS. A. Context and Motivation Traffic safety at signalized intersections remains a critical concern in urban planning, as intersections present challenges of high vehicle conflict and elevated accident risk. Large and open intersections, in particular, present challenges due to increased vehicle maneuvering space, multiple conflict points, and reduced natural traffic control, which leads to higher speeds and greater uncertainty in driver behavior.

I'm taking over the newsletter this week to tell you about the first and largest police drone operation in the country. It's a trend in policing that could hit the skies over your streets soon. Since 2018, police in a border city in California called Chula Vista have been dispatching drones to investigate thousands of 911 calls. The drones are equipped with high-resolution cameras and powerful zoom lenses, recording everything in their path. They routinely fly over back yards, public pools, schools, hospitals, mosques, and even Planned Parenthood, in the process amassing hundreds of hours of footage above residents who have nothing to do with a crime.

The use of police drones is "poised to explode" in the next year as law enforcement takes advantage of the technology's proliferation, leaving public regulation and transparency efforts in danger of being caught woefully behind, civil rights advocates warn. "A world where flying robotic police cameras constantly crisscross our skies is one we have never seen before," Jay Stanley, senior policy analyst with the American Civil Liberties Union, wrote in a report released Thursday. "Yet there are strong reasons to believe that such a world may be coming faster than most people realize." At least 1,400 police departments across the country are using drones in some fashion, but only 15 have obtained waivers from the Federal Aviation Administration to fly their drones beyond the visual line of sight, or BVLOS, of operators. That means the vast majority of departments are still limited in the types of calls they can respond to with drones.

In the skies above Chula Vista, California, where the police department runs a drone program 10 hours a day, seven days a week, it's not uncommon to see an unmanned aerial vehicle darting across the sky. Chula Vista is one of a dozen departments in the US that operate what are called drone-as-first-responder programs, where drones are dispatched by pilots, who are listening to live 911 calls, and often arrive first at the scenes of accidents, emergencies, and crimes, cameras in tow. But many argue that police forces' adoption of drones is happening too quickly. The use of drones as surveillance tools and first responders is a fundamental shift in policing, one without a well-informed public debate around privacy regulations, tactics, and limits. There's also little evidence available of its efficacy, with scant proof that drone policing reduces crime.

Chula Vista was the first police department to be awarded such a waiver. Now roughly 225 departments have them, and a dozen of those, including Chula Vista's, operate what are called drone-as-first-responder programs, where drones are dispatched by pilots, who are listening to live 911 calls, and often arrive first at the scenes of accidents, emergencies, and crimes, cameras in tow. The FAA is widely expected to fully legalize BVLOS within the next few years, which would make it easier for other such programs to launch; the sheriff-elect in Las Vegas, Nevada, already announced plans to pre-position hundreds of drones citywide to respond rapidly to crimes and shootings. New technologies such as autonomous flying, where drones can fly pre-programmed routes or respond to commands without the need for human operators, aren't far away. "This is rapidly escalating," says Matt Sloane, founder of Atlanta-based Skyfire Consulting, which helps train law enforcement agencies on the use of drones.

This article is part of the Policing and Technology Project, a collaboration between Future Tense and the Tech, Law, & Security Program at American University Washington College of Law that examines the relationship between law enforcement, police reform, and technology. There's a man pacing back and forth in the grocery store parking lot, evidently agitated, shouting at the sky. On the phone, a police dispatcher reassures you that someone is coming over to help--and so is a drone. Soon, you hear the telltale buzz of a drone overhead. Through its camera, someone is watching the agitated man in the parking lot, feeding information back to emergency services.

In 2019, the border town of Chula Vista, about 15 minutes from Tijuana, became California's first " Welcoming City," highlighting the city's financial and educational opportunities for immigrants. It's also one of the nation's most surveilled cities, where the police department uses license plate readers, drones, and body cameras to track residents and has explored facial-recognition technology. Now, those distinctions are clashing, as residents and activists accuse city leaders of "betraying" immigrant residents by permitting federal immigration authorities to access data from license plate readers. That's sparked a citywide movement questioning the city's police department, its surveillance apparatus, and its relationship with residents and immigration enforcement. Since 2015, the Chula Vista Police Department has quietly amassed surveillance tools as part of a smart city approach to policing.