It is recognized that the nature of Earthquake motions, and hence their effect on structures is dependent to a large degree on the subsoils through which they pass, This paper presents the results of a computer investigation into the effects of surface layering at the site of a proposed motorway bridge. Dynamic strain controlled triaxial tests were conducted to determine the stress-strain relationships of the soils encountered. It is concluded that the site characteristics determine the seismic response and thus control the shape of the surface motion response
 spectrum.