Are High-Speed Rail Lines Really Shortening Distances?

High-speed rail (HSR) is reshaping how we travel. Today, the longest network is in China, followed by Spain, Japan, France and Italy, while new sections are emerging in Morocco and Saudi Arabia. The goal is simple: cut travel time between cities by tackling two key factors – distance and speed.

A recent study compared HSR line lengths with conventional routes and the straight‑line distance between terminal stations. The findings reveal that new lines are increasingly close to the direct distance, almost as if the train were flying over the ground. This shortening isn’t just about saved kilometres; it makes trains more competitive against planes and cars, promoting greener transport.

Researchers examined European HSR data, building a model that contrasts three measures: HSR length, traditional line length, and straight‑line distance. The model confirms that HSR significantly reduces the travelled distance, edging ever nearer to the most direct path.

These insights can guide policymakers in planning new routes, helping them choose more efficient paths and lower environmental impact. Future studies on Asian networks could broaden our knowledge and further refine sustainable transport design.

The model introduced in the study relies on a planimetric analysis using geodetic coordinates of the terminal stations to calculate three key metrics: (i) the actual length of the HSR line, (ii) the length of the corresponding conventional line, and (iii) the Euclidean (straight‑line) distance between the two points. Researchers employed Geographic Information Systems (GIS) and curve‑level calculation software, achieving sub‑meter precision.

The main indicator is the "shortening ratio" (SR), defined as SR = (L_conv - L_HSR) / (L_conv - D_crow), where L_conv is the conventional line length, L_HSR the high‑speed line length, and D_crow the crow‑flight distance. An SR close to 1 indicates the HSR approaches the most direct possible route, while lower values signal deviations caused by topographic or urban constraints.

Results show average SR values above 0.85 for the European lines examined, suggesting design choices favored nearly linear routes, reducing tight curves and detours around natural obstacles. Moreover, a positive correlation emerged between SR and maximum operating speed: lines designed for 350 km/h tend to have higher SR than those limited to 250 km/h, as higher speeds demand more direct paths to preserve energy efficiency.

Environmentally, reduced travel distance translates into lower electricity consumption per kilometre, thanks to decreased aerodynamic resistance and fewer frequent accelerations and braking events. This impact can be quantified via the CO₂ emissions per passenger‑km index, which in lines with SR > 0.9 is 15‑20% lower than in more winding lines.

Finally, applying this model to Asian networks—where geographic conditions are more varied—could uncover further optimization opportunities, especially in mountainous or desert contexts where topographic deviations are pronounced.