You don't need to get multiple I-Pass transponders. Illinois allows registration of multiple vehicles to one transponder, we have 2 cars and one motorhome registered to ours. Vehicle license plate numbers and vehicle descriptions are entered in the system. They have velcro type attachments to allow you to move the transponder between vehicles.
I know it's not in fashion to praise governments, but Illinois really did the tolling thing right when they upgraded to join the EZpass system. They remodeled their toll plazas and established an "open road tolling" system where you no longer have to stop at a toll booth to pay a toll. Traffic backups are reduced and you can often breeze through tolling stations at highway speed.
The system reads the transponder, license plate and counts axles and then charges the corresponding account. During the pandemic it has allowed them to eliminate person to person contact by closing manned toll booths and allowing people who don't have transponder to pay tolls online (the system has recorded your license plate to catch people who try to game the system)
Living in the area, it has made travelling around Chicago much easier. USUALLY.
