Two delivery robots from two companies, Serve Robotics and Coco Robotics, collided with a CTA bus shelter in March in Chicago. The University of Pennsylvania study suggests improvements to improve internal sensors and address the optical illusion that makes clean glass harder to see than a dirty surface. The first collision occurred on March 22 when a Serve Robotics delivery robot went through the glass of a bus shelter, causing visibility issues and operator error. The study suggests improving internal sensors, addressing optical illusions that cause clean glass to be harder to distinguish from dirty surfaces. The second collision involved a combination of environmental conditions and human error. Both companies use 360-degree cameras, laser sensors and artificial intelligence to respond to real-time conditions.