AA Roadwatch say excess surface water and flooding have been reported
Drivers are being used to take extra caution on the roads, as a weather warning remains in place.
The status yellow rain warning for Munster and Leinster is in effect until 9.00pm on Wednesday.
Met Éireann says heavy rain will continue for many parts of the country, but it will gradually ease from the north through the day.
It will still be mild for much of the time, with highs of 9 to 12°C - but turning colder everywhere by the evening.
Rainfall totals of up to 40mm are expected, but larger totals are possible on higher ground.
AA Roadwatch say flooding and very wet road conditions are causing very heavy traffic and disruption in Dublin.
Excess surface water and flooding have been reported in many places.
People are advised to leave plenty of extra time for their journey, slow down and remember that stopping distance is longer in wet conditions.
And gardaí have issued an update on conditions:
Brian Farrell is the communications manager with the Road Safety Authority (RSA).
He has this advice for drivers: "The general advice on wet roads for drivers is to slow down, because you're to need extra time and distance to stop your car in the event of an emergency.
"The added risk we're getting from the downpour is the chance of spot flooding - and really the advice of driving through flooded roads is simply don't attempt to do it.
"Flooded roads can be shallower than you actually think.
"You don't want to damage the engine irreparably, and that's what you risk if the road is actually deeper than you think it is."
"And importantly when you don't through some wet roads and partially-flooded roads, just make sure to tap on the brakes after you come out of the water just so that you can get rid of any water on the brakes".
Commuters are being advised to check with Met Éireann, the AA, local councils and the gardaí for any traffic updates before making their journey home.