Unclear signage and a lack of consistency could be factors leading to motorists overpaying at toll booths, according to a transport expert.
Ireland's tolled motorways are run by a number of different companies which has lead to a lack of consistency.
New figures in the Irish Independent show over 800 thousand euro 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 thousand euro in cash left behind.
Associate Professor at Trinity's School of Engineering, Brian Caulfield, says some toll booth accept contactless payment while others accept change.
The result of this lack of clarity in signage means that motorists are unsure as to how much they should pay and what category do they belong to.
