What are the necessary structures for transportation?

Necessary structures for transportation include roads, bridges, railways, airports, and ports, which facilitate the movement of people and goods. Additionally, infrastructure such as traffic signals, signage, and maintenance facilities play critical roles in ensuring safety and efficiency. Effective transportation systems also require logistical hubs like warehouses and distribution centers to manage the flow of materials. Overall, a well-integrated network of these structures is essential for a functional transportation system.