Best flat route south Dublin for intervals

N81 isn't bad for a solo rider or you could do the small Blessington lake circuit.

If you want to stay in Rathfarnham, I got great Covid flat training out of a local circuit. Anticlockwise so junctions are roundabouts or yields. Some pedestrian lights that you can get caught at but it wasn't too bad. You'd have to time it right though cos obviously at peak traffic times it's poxy.

So if you know Buglers pub on Ballyboden road, say you start there. Go down to the junction and turn left onto Ballyroan Rd. Left onto Firhouse Rd, left again onto Knocklyon Rd. Jink left onto Templeroan Rd and then left at the roundabout onto Ballyboden way, down to the roundabout and left and you're back at Buglers.

Iirc it's a 5k lap. I did 100km on it at least once during the strict Covid boundary restriction. :)

Of no benefit but until about 10 years ago anyone could use the velodrome like cycle track in Sundrive Park. Was great of a nice evening to head down for an uninterrupted hour's time trial on a lovely smooth tarmac surface. That was until scumbags loaded a number of plastic barriers onto the track and set them alight damaging the surface for all. An expensive repair and repercussions resulted in 3 meter high barriers all round and no access for anyone unless an accredited member of a time trial club and even then only during club hours. Just can't have nice things in Ireland with wanton vandalism.

Maybe head toward tallaght then the jobstown to lucan stretch? The R136, It's relatively quiet, decent surface, huge bus lanes, roundabouts and even a cycle lane. Would sandyford to enniskerry be too hilly?