During the Spring and Autumn Period and the Warring States Period, wars were frequent among countries, commercial circulation was more developed than before, and all countries vigorously developed transportation.
In the second year after Qin Shihuang unified the six countries (220 BC), he ordered to build the equator (the main road connecting the Central Plains and the southern region) throughout the country, and later ordered to build a straight road. The construction of equator and straight road is a large-scale road construction project in Qin and Han dynasties, which is objectively of great significance to promoting the development of land transportation, cultural exchange and ethnic integration.
Chidao in Qin dynasty
Chidao, also known as Imperial Road, is a special road for the emperor to patrol. According to Hanshu, Qin Chi Road is flat, with a width of 50 steps (about 69 meters today), and a tree is planted every three feet (about 7 meters today). Both sides of the road are rammed with metal cones, and in the middle of the road is a car for the emperor to patrol.
Qin Chi Road probably has a track, and its principle is the same as that of modern railways. There are not only subgrade, but also tracks and sleepers, and there is a reversing system between tracks for cars to change tracks. The wood used for track is hard and durable, while the sleeper is soft and can be closely combined with the hard subgrade.