Taxpayers will have to compensate the operators of the new M3 motorway if the number of motorists using the road falls below agreed targets.
For the first time, the National Roads Authority has agreed a "minimum traffic level" in its contract with the toll company Eurolink.
If traffic falls below expectations, the State will have to make up the shortfall in payments to the firm.
The NRA says the agreement is necessary to attract private investment in the project.
The controversial €650m motorway, which passes through the Tara-Skryne Valley in Co Meath, is due to open in the middle of next year.