There are only two cities that have international air connections among all cities along the Silk Road in China. These are Xian and Urumqi. To other cities, people need to take train and most of the time by road.
Xinjiang has a vast desert territory, the Gobi desert, marshy grasslands, valleys, forests, which makes road travel not so conducive. The roads in Xinjiang are just normal as in other cities; however in some remote areas, they are poorly maintained. The ride might become too bumpy in remote areas and driving takes relatively long between cities.