Beijing is a communication hub with roads, highways, railroads and flights connecting all parts of China as well as all the major cities around the world. It is also the popular destination of many international flights to China. There are six ring roads circling the city of Beijing. Beijing is easily accessible with nine expressways, eleven China National Highways and several railway routes starting from Beijing. The Beijing subway is a rail network that's the most convenient and affordable form of transportation. Travelling around Beijing by bus is also the most common public transportation available. Beijing is also a city filled with bicycles, which is the primary mode of transportation used in Beijing.