This paper explores the role and capacity of strategic level assessments in addressing the strategic dimension of High Speed Rail (HSR) proposals and influencing decision-making processes. The overall research objective was to find out to what extent opportunities for strategic thinking are being undertaken in HSR. Three different cases of high speed rail were compared – High Speed Rail 2 (HS2) in the UK, High Speed Rail Network (RFAV) in Portugal and European Gauge Railway Line Kaunas in the Lithuanian-Latvian Border (Rail Baltica 2). Strategic environmental assessment (SEA) effectiveness literature was reviewed to draw on criteria that could establish a comparative framework to explain how environmental and sustainability assessments were undertaken in the three aforementioned European high speed rail case studies. Research results allow us to conclude that an SEA or a sustainability assessment/appraisal (SA) will be most beneficial if developed before any HSR project to first determine if HSR is really necessary and strategically justifiable to the achievement of both environmental and sustainability objectives. Results achieved suggest that even though the SEA and SA in the three cases studied can be said to have influenced the planning process mostly at project-level decisions, it also shows a missed opportunity to contribute to developing a high level strategy for HSR that addresses several strategic issues, assessing options before they are undertaken.