Speed limits in Ireland have undergone many changes since first introduced, most notably in 2005 when the State adopted metric speed limits. The challenge presented to the Department of Transport, Tourism and Sport and Local Authorities is to assess, manage and implement a system of speed limits that are appropriate, credible, transparent and have the support and respect of the road user. Until 2005 a National Speed Limit applied to all roads outside built-up areas. Metrification then occurred, and the National Speed Limit was replaced by a system of Default Speed Limits that were assigned to each class of road. Over time, this led to a lack of credibility and inconsistency in the speed limit system. This thesis presents a history of how Irish speed limits have evolved and how they are currently set and looks at Ireland’s collision history, its speed limits and its road safety performance in relation to other European countries. Current speed limit assessment methods, both in Ireland and in other jurisdictions, are also presented. An alternative means of assessing the appropriate speed limit for rural single carriageway roads is proposed by deriving a Safe Profile Velocity (Vsp) and an Efficiency Index value for the road or section of road under assessment, by capturing actual driver behaviour - the hypothesis being that the derived Safe Profile Velocity (Vsp) reflects what is occurring on the road and simplifies the assessment method in relation to current methodologies like the Speed Assessment Framework, while retaining core principles. A simplified assessment method is becoming increasingly necessary as Local Authority resources are limited, but demand for a credible speed limit system remains. This thesis contains seven case studies and shows the relationship between the Safe Profile Velocity (Vsp) and existing speed limits - the Efficiency Index, and shows the effect on this Index should the speed limit be altered. The question of considering the use of speed limit values that do not currently exist in legislation also emerges within this thesis. Areas where future analysis or further research may be beneficial are also proposed.