[1][2] The first section of the route starts from the N3 and closely follows the River Tolka through Dunsink, Scribblestown, and Ashtown.

It then hugs the border of Tolka Valley Park until it reaches the R135 in southern Finglas.

The R102 resumes after the traveller has gone 230 metres south on the R135 (Finglas Road) to join the second section of the route.

The second section begins heading east on the Old Finglas Road.

A brief 200 metres swing to the north along Tolka Estate and a turn to the east takes the road to Griffith Avenue.