I was curious about this myself.
found this link
Description of the Nature and Extent of the Proposed Development and the Principal Features thereof: -
1. The construction of 1,160 m of four-lane carriageway from the Ongar Road in a south-westerly direction to tie in with the existing R149 Lucan Clonee Road at Barberstown Lane South.
2. The proposed new carriageway includes for 2 number 3.5 metre wide all purposes vehicle lanes, 2 number 3.0 wide metre bus lanes together with a central reservation 2.6 metres wide inclusive of a containment road safety barrier divide. The scheme also includes for footpaths, cycle tracks, grass verges, surface water road drainage, public lighting, landscaping and boundary treatment on both sides of the new road.
3. The provision of a new signalised Junction with right turning lanes at the proposed entrance to the SDZ lands and the proposed site for the primary and post primary school sites.
4. The construction of a new railway crossing south of the proposed SDZ lands and re-alignment of the existing 110 KV ESB overhead lines.
5. The construction of a 70 metre Inscribed Circle Diameter Roundabout adjacent to the junction of the Lucan Clonee Road and Barberstown Lane South.
6. The construction of 700 metres of 9.0 metre wide all-purpose carriageway together with 2 No. 28 metre Inscribed Circle Diameter Roundabouts inclusive of revised access accommodation works together with footpaths, cycletracks and grass verges on both sides of new road along and abutting Barberstown Lane South from Roundabout referred to at No. 5 above and as shown on sheets 3 and 4 of public display drawings.
7. The construction of 285 metres of 7.0 metre wide carriageway northwards along the Lucan Clonee Road from Roundabout referred to at No. 5 above together with grass margin, footpath, cycle track and boundary treatment on eastern side of new road.
8. The construction of 200 metres of varying width of carriageway southwards from Roundabout referred to at No. 5 above together with a right turning standing lane to tie into existing Lucan Clonee Road and junction at Passifyoucan.
9. Re-location of existing services in the area of the proposed works to accommodate surface water drainage, public lighting & ducting in the realigned section of road.
10. Provision of the appropriate road signage and lining.
The Ongar to Barnhill Distributor Road is the most northern section of a future link from Ongar to the N4 as identified in the County Development Plan 2005-2011. It is predicted that this route will replace the existing R149 Lucan to Clonee when complete.