The Road Safety Authority (RSA) has sent a written request to the National Roads Authority (NRA) to ask for clarification on how drivers who need to stop on the main motorways will be catered for.
The RSA wrote to the Roads Authority following the NRA's decision last December to drop a proposal to build 11 rest areas along the motorway network.
This decision means the NRA will concentrate instead on the provision of 12 fully-serviced stations, effectively halving the number of places where a driver will be able to stop on the motorway network.
The planned service areas will provide fuel, food and extensive parking.
Each service area will either have facilities on both sides of the road or will be accessible from both sides.
The RSA is concerned about how fatigue affects drivers on Irish roads; it believes that fatigue may be a factor in one in five fatal crashes.
In particular, it is worried about the impact of fatigue on lorry drivers, 60 per cent of whom the RSA estimates are breaking regulations governing how long they can drive between rest periods.
Speaking before the Oireachtas Transport Committee recently, Noel Brett, the head of the RSA, said the issue had wider implications than just driver fatigue.
He said motorists needed both serviced and unserviced areas along major routes where they could stop to take a phone call, change driver, rest or use a toilet.
Mr Brett added that the survival time for a car that stops on the hard shoulder to attend to a child "is very low".
Traditional lay-bys used by trucks on major national routes were being closed off, further reducing the number of places where a lorry can stop safely, he said.
In towns and villages where these areas had been closed off, they should be reopened, Mr Brett said.
The Committee was told that the estimated survival time for a vehicle on the hard shoulder of a dual-carriageway before being rear-ended is 10 minutes, according to research from the UK.
"The hard shoulder is not a safe place to be, and in fog or adverse weather conditions other drivers will instinctively follow the red lights of someone stopped on a motorway," said Mr Brett.
"People follow a car onto the hard shoulder and rear-end it," he said.
Mr Brett said he had written to the NRA twice about the issue of rest areas in recent weeks, asking specifically about unserviced rest areas in the second letter.
The NRA maintain that it had opted against rest areas - which would have been a lay-by with toilet facilities - due to concerns over anti-social behaviour at similar, unmanned areas in other countries.
