The controversial M3 motorway in Meath, which critics warned was too expensive and surplus to the country's transport requirements, will cost the taxpayer almost €50m in penalty payments because not enough drivers are using it.

The information is contained in a report issued by environmental group Plan Better, which also says the collapse in traffic volumes during the recession has left us with a series of "ghost roads". Some proposed new motorways will not be needed for another 40 to 50 years, according to the research.

According to the group – a joint initiative of An Taisce, Friends Of The Earth, Friends Of The Irish Environment and Feasta – the taxpayer could face a bill of a minimum of €100m for the National Roads Authority (NRA) to compensate the consortiums that built road projects such as the recently opened M3 from Clonee to Kells and the Limerick tunnel.

Dr Miles Deas, who carried out an extensive study of road traffic levels for Plan Better, has calculated that the penalty payment the NRA will have to pay to the Ferrovial construction firm, as a result of traffic levels being 5,000 cars a day below target on the M3, will most likely be in the region of €47.76m.

The penalty for the new Limerick tunnel toll not reaching its expected traffic targets could leave the taxpayer with a €77m penalty for the NRA to pay to the tunnel operators, Direct Route.

"I received information regarding the recently opened M3 Clonee-Kells and Limerick Tunnel PPP (Public Private Partnership) toll contract. They show how over-optimistic traffic forecasts will result in actual traffic falling short of contractually guaranteed levels," Deas said.

"The result will be year-on-year penalty payments by the Irish state to these private firms. The contracts are naive in that there is no amendment or reset clause... We have lurched from sublimely bad roads to the ridiculously grandiose."

The Plan Better group also advocates an urgent revision of the country's road-building programme. The group's co-ordinator, James Nix, a former Green party councillor who left the party, has labelled the NRA's proposals for expansion of the roads "a charter for misspending".

"The NRA's current plans assume high levels of perpetual growth. All of the current plans assume robust economic growth will return next year so the projects should be reviewed," said Nix.

The NRA has planned a stretch of motorway from Oilgate in Wexford to Rosslare Harbour but Nix believes, in view of the traffic levels on the road, "it is obvious that a motorway is not needed there for another 40 to 50 years".

Similarly, the NRA plans to build 80km of motorway from Limerick to Cork via Charleville. Nix argues that a "much more sensible proposal is to build 55km of motorway from Limerick to Cahir, where the road would be tied in with the existing Dublin to Cork motorway. The saving here would be €250m as every kilometre of motorway costs about €10m."

Plan Better also disagrees with the state's plans to pledge €500m to build a motorway through the North from Monaghan to Derry.

"Along that entire route from Monaghan to Derry, we currently have approximately half the traffic threshold to justify a motorway," said Nix.

The NRA says revenue-guarantee arrangements are a common feature of PPP contracts throughout Europe and no penalty payments have yet been made to roads consortiums in Ireland.