Denver International Airport uses many pneumatic tube systems, including a 25 cm diameter system for moving aircraft parts to remote concourses, a 10 cm system for United Airlines ticketing, and a robust system in the parking toll collection system with an outlet at every booth.
Note: No citation, and I can't find any reference to it on the web.
Question: If these systems actually exist, what are their total lengthes (eg. 35 km total) and usage rate (eg. 7000 objects per day)?
According to the Public Relations Department at the Denver International Airport, as of May 24, 2019 there is no such pneumatic tube system at the airport.
Thank you for contacting Denver International Airport. We have
evaluated your email. I spoke with airport operations to find out if
they had any information on using a pneumatic tube system and they
advised me they do not. We do appreciate your feedback.
Thank you, kindly, for bringing this matter to our attention.