This paper describes the methodology that was developed for a series of engineering geological constraints studies for highway schemes inIreland. These comprised the synthesis of findings from two main study elements; an initial desk study review of published information sources and the results of a terrain systems mapping study for areas up to 600 km2. The main requirement was to identify, classify and delineate those potential geomorphological andengineering geological constraints to possible highway route corridors.

A case study for the N6 Kinnegad to Athlone Dual Carriageway is presented which includes the published sources that were reviewed and information obtained, and the initial terrain systems mapping exercise that was undertaken. Fourteen different terrain units were identified and their distribution was presented on 1:50 000 scale drawings. Characteristic physiography, materials, resources and constraints associated with the terrain units were presented in summary tables. The relative constraints to highway design and construction were also presented on a series of 1:50 000 scale derivative drawings. Four route corridors that were considered the most viable from understanding of the engineering geological constraints and other factors including; archaeology,environment, and traffic were developed and formedthe basis for more targeted desk studies and fieldassessment, and the design of a preliminary ground investigation.

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