Labour and the Liberal Democrats have pledged to scrap tolls on the Tay Bridge and remove some charges on the Forth road crossing.
Labour said the Tay Bridge was important to the local economy
Tolls for cars with more than one occupant on the Forth Bridge would be scrapped under their plans.
The SNP, who are committed to abolition of all bridge tolls, claimed their pressure had led to a Labour U-turn.
Scottish Labour leader Jack McConnell said the Tay move would tackle congestion in Dundee city centre.
He said: "We have been considering the impact on the Fife economy, and on traffic congestion, of changing the current tolls.
"I am still concerned that removing tolls completely on the Forth Bridge could lead to increased traffic congestion.
"Ending the revenue stream from tolls before detailed costs and proposals are prepared for a new crossing of the Forth is simply irresponsible."
He added that providing an incentive for people to car-share would cut congestion and may help to extend the life of the current road bridge.
The SNP, Mr McConnell claimed, were incapable of taking difficult decisions and were acting irresponsibly when it came to protecting the environment and controlling government spending.
A Scottish Liberal Democrat spokesman said party leader Nicol Stephen was determined that its manifesto was "fair and effective".
"That is why it will commit the Liberal Democrats to abolishing tolls on the Tay bridge and ending them on the Forth bridge for cars with more than one occupant," said the spokesman.
"We will ensure the replacement Forth crossing is built as soon as practicable, with special provision for public transport such as light rail and bus."
A Holyrood debate earlier in the year on scrapping tolls on the Forth and Tay road bridges ended in stalemate when the parliament failed to agree a position.
The result came after Labour and Liberal Democrat MSPs from the east coast spoke out against the charges.
SNP Dundee East MSP Shona Robison said Mr McConnell was now panicking under pressure from her party and had been "forced into following where the SNP has led".
Labour has decided against scrapping all charges on the Forth
"He has had five years to scrap tolls, and has done nothing about it, which makes this another empty promise," she said.
"People know that only an SNP government can be trusted to scrap the tolls."
The tolls commitment came as Scottish Labour was putting the finishing touches to its manifesto.
Campaign group, the National Alliance Against Tolls Scotland (Naats) said Labour's toll plans for the Forth Road Bridge were "insane".
"Congestion is caused by the inadequacies of the A8000/M9 spur and by the toll collection itself," said a spokesman.
The group also claimed that keeping Forth tolls because of the prospect of a new road crossing was a red herring, as such a move may be privately financed and tolled.