Poor signage and a lack of consistency could be factors leading to motorists overpaying at toll booths, according to a transport expert.
New figures in the Irish Independent show over €800,000 was overpaid at tolls across the country in the last two years, due to drivers leaving their change behind.
The M1 was the most lucrative road for excess tolls, with €143,000 in cash left behind.
Associate Professor at Trinity's School of Engineering, Brian Caulfield, says a number of factors could contribute to this:
"There's maybe a lack of consistency and that drivers are not fully aware or prepared for the tolls coming up.
"A lot of our tolls across the company are operated by separate companies, and what they accept at each toll bridge is different.
"You could have contactless card at one, coins at another or tags as well."