These are major (some toll) truck routes, primarily intended to connect Beijing with the rest of China.
China National Highway 112, despite being a series-100 China National Highway, does not begin Beijing, but begins in Gaobeidian and forms a long ring route.
The 'G' in front of the highway route numbers stands for 国 (pinyin: guó), meaning nation or country.
The eleven China National Highway routes depart from Beijing in a spread of compass directions: 813 kilometres of the system lies within Beijing municipality.
Tiananmen is considered "km 0" for all China National Highways.