(a) Metalled roads are all weather roads, whereas unmetalled roads are difficult to use in the rainy season, as their upper surface becomes uneven due to absorption of rain water.
The reason is that metalled roads have a waterproof coating on the upper surface, making them usable in all seasons.
(b) Border roads Many border roads are of strategic importance in the border areas. They have improved accessibility in areas of difficult terrain and helped in the economic development of the border areas of the country.
National Highways link important parts of the country like state capitals and commercial centres. They enable fast and efficient
movement of goods in areas connected to them.