Cardiff Council issued £5.6 million pounds in bus lane fines last year, the second highest in the country.
Figures obtained through a Freedom of Information request by comparison site Confused.com show only Glasgow Council issued more fines. Across Wales as a whole, Cardiff made up the most penalties issued. Approximately 95% of bus lane fines in Wales were issued by Cardiff Council.
In a survey 62% of motorists in Wales who were hit with a fine said they were confused and drove in a bus lane unknowingly.
Some drivers are now calling for the money made from bus fines to be put into making bus lane signage clearer, and say this may reduce the amount of confusion.
A spokesperson for Cardiff Council said the income from bus lane fines already "funds the operational cost of parking and enforcement." The council said any additional profit is put into a "parking reserve account" used "to support transport services, off streeting parking and highway improvements."