Motorists may be asked to voluntarily obey new speed limits on the country's busiest motorway because there is no law for gardaí to enforce them.
Variable speed limits will be introduced on the M50 next year. Overhead warning signage is going up shortly, testing will begin in the new year and the new speed limits will follow on a staged basis.
The southern section will have them first but ultimately the new regime will apply along the M50's entire length.
Transport Infrastructure Ireland (TII) has taken the decision to press ahead with the plan despite the likelihood that there will be no penalty for breaking the limits. A bill to make variable speed limits legally enforceable has been delayed by Brexit and other Government priorities.
TII spokesman Sean O'Neill said they would be "advisory speed limits" until such time as they were enforceable by law.
"We're hopeful people will abide by them and once they understand why we have them, they'll see they make sense."
Variable limits allow speed limits to be reduced to take account of bad weather and congestion. Mr O'Neill said keeping all vehicles moving at a slower but steady pace in such conditions helped everyone move faster.
Variable speed limits have been discussed by government since 2013, but the underpinning legislation has been put on the long-finger.
The Department of Transport said progress was being made. "The minister has indicated that progressing the Road Traffic (Miscellaneous Provisions) Bill is a priority for the remainder of 2019, and it is hoped to publish the bill by the end of the year," a spokesperson said. Enacting the bill could take much longer, but AA consumer affairs director Conor Faughnan welcomed the decision to go ahead without it.
"It would be better if the legislation was in place along with the technology, but I think TII is taking the right attitude because this has been talked about for years," Mr Faughnan said.