I-PASS customers traveling without a transponder properly mounted in their vehicle will be charged the cash toll rate after accruing an excessive amount of tolls in a month starting next year, the Illinois Tollway said Friday.

The agency is encouraging I-PASS users to always drive with a transponder properly mounted in their vehicle when they travel on the Tollway to ensure they continue receiving the 50 percent discount on tolls.

For I-PASS customers who already drive with a transponder mounted in their vehicle, nothing will change and tolls still will be assessed at the discounted I-PASS rate.

The majority of I-PASS customers who already regularly use transponders on the Tollway will not be affected.

The Tollway encourage I-PASS customers to obtain a separate transponders for each vehicle registered to their account so they don’t have to remember to transfer a transponder to the vehicle they are driving on the Tollway.

Transponders can be shared between cars and motorcycles registered to the same I-PASS account, but sharing a transponder puts drivers at risk of forgetting to move the transponder, the agency said.

The I-PASS Shared Balance allows all transponders to draw from the same, single prepaid account balance, which means I-PASS users will not need to maintain a separate balance for each transponder.

Additional transponders can be obtained from the Tollway for a $10 refundable deposit by ordering online or visiting a customer service center. Transponders at Jewel-Osco are pre-programed with the $10 deposit and $20 in tolls, according to the Tollway.

When I-PASS users travel through toll plazas without a transponder in their vehicle, the Tollway uses video tolling – which matches digital images of license plates to I-PASS accounts – to deduct the tolls from customers’ accounts, the agency said.

Processing video tolls costs the Tollway about 23 cents per transaction, nearly three times more than processing transponder transactions, which cost about 8 cents per transaction, according to the Illinois Tollway.

Encouraging I-PASS customers to always travel with a transponder in their vehicle helps the Tollway operate more efficiently by keeping its administrative costs as low as possible while still providing the best service possible to its customers, the agency said.