My understanding of this without double checking is:
A) A where is there is a cycle lane it must be used. I know someone who got a ticked for not using it on the Stillorgan dual carriageway AKA the N11.
B)It is illegal to cycle more than two abreast, and you can only do so when it is safe.
Now to find that copy of the new rules of the road...
Towger
The double check came up this this:
Cycle tracks
A cycle track or lane is a reserved part of a roadway for bicycles (not motorcycles) and can be either:
• mandatory, or
• non-mandatory.
A mandatory cycle track is bordered by a continuous white line on the righthand side. It is only for bicycles and motorised wheelchairs, so no other drivers may use it or park in it.
A non-mandatory cycle track has a broken white line on the right-hand side. The cyclist may leave this type of cycle track if:
• they have already indicated they want to change direction,
• a bus is letting passengers on or off at a bus stop located beside the track, or
• a vehicle is parked in the track while loading or unloading.
Mandatory cycle tracks are reserved 24 hours a day, unless an upright information sign at the start of and/or the side of the track shows another period of time.
A cycle track can also be a reserved part of a footpath or other area off the road.
A cyclist must use a cycle track if it is provided.
If a cycle track is two-way, meaning bicycles travelling in opposite directions at the same time can use it, cyclists should stay as near as possible to the left-hand side of their track.
You must obey cycle track lights.
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Two abreast
Do cycle in single file if cycling beside another person would endanger, inconvenience or block other traffic or pedestrians.
Don't ever cycle side-by-side with more than one cyclist.
Do cycle in single file in heavy traffic.