It looks like the rear wheels can moved up and down to give it more ground clearance for sidewalks. I presume it only works in areas that are wheelchair access

It looks like the rear wheels can moved up and down to give it more ground clearance for sidewalks. I presume it only works in areas that are wheelchair accessible, and any areas it has trouble with (such as a flight of stairs in an apartment), it could notify the recipient to come and collect it.