Delivery robots still learning from 'edge cases,' scientists say

Delivery robots have some growing up to do.

That’s the consensus among scientists and engineers who were analyzing the safety and efficiency of this developing technology before two of the robots crashed into a CTA bus shelter in March.

A 2025 study from engineering experts at the University of Pennsylvania may have some solutions. They include improving complex internal sensors and addressing the simple optical illusion that makes clean glass harder to see than a dirty surface.

Vijay Kumar, dean of engineering at the University of Pennsylvania, compared the delivery robots to self-driving cars that encounter “edge cases” — things that software developers and simulators haven’t yet modeled.

“There are millions of things that can go wrong and will go wrong,” Kumar said. “It’s really hard for robot software developers, for folks like me [in] academics to predict because the environment is indeed very unstructured.”

The first collision occurred March 22, when a Serve Robotics delivery robot went through the glass of a bus shelter in West Town near the intersection of North Racine and West Grand avenues.

On March 24, a second delivery robot — this time from Coco Robotics — collided with a bus shelter near North Larrabee Street and West North Avenue in Lincoln Park.

Video of the crashes went viral.

Though one of the companies had their robot "apologize" through an ad on a bus shelter, the malfunctions are no laughing matter, according to critics.

“My first reaction both times when I saw the imagery is thankfulness no one got hurt,” said Josh Robertson, a North Side resident who started a petition to pause a trial program the city began in 2022 until after a public hearing. “I’ve got a couple of kids, and many Chicagoans have kids or pets, and if someone had been on the other side of that glass, these would be much different stories.”

Coco robots use 360-degree cameras, laser sensors and artificial intelligence to respond to real-time conditions. Serve uses AI, computer technology and a number of different sensors. Both also enlist remote human operators who monitor and help control the robot’s movements.

Visibility factored in both collisions. In the first crash on March 22, three internal sensors failed simultaneously, and video from that Serve robot’s point of view showed the bus shelter’s glass was difficult to see, said Ali Kashani, CEO of Serve Robotics.

And in the crash on March 24, visibility issues mingled with human error, according to Carl Hansen, a vice president and head of government relations at Coco Robotics.

“Based on our review this was caused by a combination of environmental conditions and operator judgment,” Hansen said. “Muted lighting due to weather conditions made the bus shelter glass difficult to detect through the robot’s sensors, and a remote operator made a decision to navigate around one of the shelter posts through the shelter.”

Kashani said Serve Robotics' delivery robots operate with a “Swiss cheese” approach involving three internal sensors and multiple cameras to ensure the robots are aware of the conditions around them. In the West Town collision, all three sensors failed simultaneously, he said.

“When you add all those pieces together, usually when one fails the others catch that failure,” Kashani said. “This is a case where all three failed and that’s why it’s unusual.”

Visual problems can stem from something as simple as the changing seasons, Kumar said. “Hard to know, but I'm willing to bet that has something to do with the variation of illumination the robot was seeing, and the reflection off of the glass or the lack thereof,” he said.

Bus shelters that collect dirt and snow on their glass during winters make them more detectable, which makes it easier for the robots to avoid, Kumar said. But a rainstorm that makes the same glass transparent can make it harder for the robot to detect.

At the time of each collision — the first one at about 4 p.m. and the second about 8:30 a.m. — the temperature was about 35 degrees and conditions were cloudy.

Malakhi Hopkins — a PhD student in the Kumar Robotics Lab — said he’s working on a visual sensor that helps robots judge the distance and angle of mirror-like surfaces.

And Hopkins is also working on an ultrasonic sensor that uses sound to help the robots better detect clear glass.

“Sound does not go through glass, so then we’re able to say, even though we have a low-density depth profile, we can still say that there is definitely something in front of you,” Hopkins said.

After the crashes, Kashani said Serve Robotics made software updates that slowed the robots down around the bus shelters.

“Knowing that [a robot] is close to a bus shelter, it can behave differently, and that’s one of the things we started immediately implementing,” Kashani said.

When complications arise, individuals monitoring the robots can step in.

In 2022, the City Council approved a Personal Delivery Device pilot program, allowing restaurants to use the small robots to deliver food.

Coco Robotics’ robots began appearing in the 27th and 34th wards in late 2024 as part of an initial pilot program. Serve Robotics, another Los Angeles-based sidewalk robotics company, launched 50 robots across much of the city’s North and West sides in September 2025. About 100 of the robots operate in Chicago, all from the two companies.

The program will not renew past May 2027 without action from the City Council. In December, the city created a 311 category to encourage Chicago residents to submit their concerns and feedback about the robots.

Kashani said he was “surprised and disappointed” when he first heard of the West Town collision but said he believes that robot deliveries ultimately make the city safer. "Every trip a delivery robot makes is one less trip a car has to make."

“We want to continue to have that really, really awesome safety record that we have today," he said. "I’m disappointed, but we learn, we improve, we apologize.”

The crash by the Coco robot “was not a sensor malfunction,” Hansen said. “We’ve followed up with our remote operator team to make clear that Cocos should never travel through bus shelters, regardless of perceived visibility, and we’ve since reinforced that protocol with additional operator training and clearer guidance to ensure this does not happen again. … Coco robots have completed more than a million miles of deliveries, and this is the first incident of this kind. We take this very seriously and are focused on ensuring it does not happen again.”

A few weeks after the West Town collision, an apologetic ad from Kashani’s company popped up at the repaired bus shelter, saying “I took ‘breaking into the market’ too literally.’ I'm really sorry about the bus stop…and the dramatic entrance. I promise to do better.”

“We made a mistake and we own it and we gotta make sure we don’t make that mistake [again,]” Kashani said.