One of the direct effects of introducing high-speed railway lines is a significant reduction in travel times between major cities. This is particularly relevant in mountain areas. It not only makes cities more easily reachable with more sustainable transport systems but can also encourage different travel behavior and reduce environmental pressures on sensitive areas. A comprehensive analysis of the spatiotemporal effects of the introduction of high-speed railways in the Alpine arc has not yet been developed. To help fill this gap, this study uses multidimensional scaling and the geographical information system to illustrate the time–space compression. This term indicates the erosion of spatial and temporal distances in the areas of the Alps directly affected by the new railway lines. Six trans-Alpine high-speed railway lines are analyzed, comparing current and projected travel times by train. A time-based map is created to show the time–space compression in every transversal direction, particularly on the French and the Austrian side of the Alps. Implications in terms of local accessibility are also analyzed, focusing on the Autonomous Province of Bolzano/Bozen-South Tyrol. Finally, the paper discusses the importance of time-based maps for the understanding of sociospatial dynamics and the possible implications for spatial development.