Operators of the Port Tunnel in Dublin have raked in more than €90,000 in excess payment since 2019.
Drivers who don't produce the exact amount at the unmanned toll booth are often overcharged because there is no way of claiming change instantly.
Motorists overpaid with coins by almost €45,000 in 2019 according to the Irish Daily Star.
Last year the figure had dropped to €19,000.
Transport Authority Ireland says the excess money is used for tunnel maintenance and other essential works.
They are also reminding drivers that you don't need to use loose change and you can pay for the toll with contactless debit or credit cards along with a prepaid toll card.
