For the most part cycling in Dublin is easy and safe to do. Lanes are clearly marked and very few roads are shared lanes but I have always found an alternate route. The only areas that are somewhat unsafe are freeway on-ramp crossings (heading south on Tassjara, Hacienda and Hopyard). There is also a spot on Fallon Road, north bound that lacks a bike lane. Overall though, cycling in Dublin is very doable and safe.