There are many linear lines because it is difficult to build many long, wide tunnels due to the issue of construction cost despite the large number of mountains (for operations of steam locomotives, it was more advantageous to avoid sharp inclinations even if the number of curves would be large; moreover, long, wide tunnels also have a problem of smoke from steam locomotives, other than issue of cost).
山地が多いが長大トンネルを建設費等を理由に多数建設できないため線形(路線)が多い（蒸気機関車の走行にはカーブを増やしてでも勾配をできるだけ避けた方が有利であった。また、長大トンネルは建設費等のほかに蒸気機関車からの煤煙の問題があった）。