On 27th June 2021, phase 1 introduced H-Spine routes (H1, H2 and H3) and Route 6.
| Route | Areas Served |
| H1 | Baldoyle – Donaghmede – City Centre |
| H2 | Malahide – Carrickhill Road – Bayside – City Centre |
| H3 | Howth – Bayside – City Centre |
| Route 6 | Howth – St. Fintan’s – Bayside – Watermill Road – City Centre |
| Day | Route | Frequency |
| Monday–Sunday | H1 | Every 15 minutes |
| Monday–Sunday | H2 | Every 30 minutes |
| Monday–Sunday | H3 | Every 30 minutes |
| Monday–Sunday | Route 6 | Every 60 minutes |
The combined frequency along the central H spine section is approximately every 8 minutes.
A Spine is a very frequent route made up of multiple bus services that operate along a shared corridor.
Radial routes are other city-bound services that operate into Dublin City Centre but are not part of a Spine. They follow their own timetables.
