The correct option is Waterways.
Explanation
The cost of transportation is determined by factors such as friction, fuel efficiency, and carrying capacity. Different modes of transport have distinct economic advantages based on the weight of the cargo and the distance to be covered.
- Waterways: Water transport is the most energy-efficient mode because water offers significantly less friction than land. It has a high load-carrying capacity, making it the cheapest mode for transporting heavy and bulky goods (such as coal, iron ore, cement, and timber) over long distances. It requires the least amount of fuel per unit of load.
- Railways: While railways are also efficient for transporting bulky goods over long distances and are faster than waterways, their operational and maintenance costs (track maintenance, fuel, rolling stock) are higher than those of water transport.
- Airways: Air transport is the fastest mode but also the most expensive. It is suitable for high-value, low-volume, and perishable goods, rather than heavy or bulky cargo.
- Pipeline Transport: Pipelines are the most convenient and efficient mode for transporting liquids and gases (like petroleum, natural gas, and water) or solids in slurry form. However, they are not suitable for general heavy and bulky solid goods, and their initial installation cost is very high.
Key Takeaway: Waterways remain the cheapest mode of transport for heavy and bulky cargo due to superior fuel efficiency and the natural buoyancy of water, which reduces traction effort.