The R418 Athy - Kilcullen road at Ballyshannon Crossroads. Formerly a section of the N78: note the section marker in place in 2010.
The R418 is a lengthy regional road in Counties Carlow and Kildare running from Kilcullen via Athy to Tullow.
It can be considered in two sections. The 19.5 km section running southwestward to Athy from a junction with the R448 at Knockaulin, 2 km south of Killcullen, was once a relatively important route, being the T6 in the 1920s numbering and later becoming the N78. With the extension of the M9 the N78 east of Athy was rerouted on to new build connecting more directly with the motorway. The R418 joins the modern alignment of the N78 at a roundabout on the outskirts of Athy.
Some 200 m closer to Athy, the original R418 then heads off again, now south-eastwards. This section extends for 13 km to historic Castledermot, passing over the M9 after 10 km. In Castledermot it joins the R448 (the original N9), and at the southern end of the main street the R418 branches off again to the south-east for a final 13-km section which ends on the R725 in Tullow.