Improving productivity in regions with declining populations is crucial for sustainability. High-speed transportation networks play a key role in boosting total factor productivity (TFP) by connecting regions and increasing knowledge sharing. Research using Japan's data shows that inter-regional networks have a bigger impact on TFP growth than regional agglomeration. By enhancing transportation connections between cities, economic benefits spread beyond urban areas, benefiting a wider geographical area. Developing high-quality transportation networks is essential for regional sustainability and expanding economic benefits across regions.