7Xu Jiajun, Cheng Wenhao, Ahn Sung Jin, Gashahun Lemessa, Hafsat Abiola-eosteno, and Kulket Tohtubtiang, "Beijing guidance information System: major problems and solutions", working paper.
8Douglas Scott, Cheng Wenhao, Dong Changgui, Kim Chulmin, and Yilak Akloweg, "Empirical study on Beijing subway system: from the perspective of user friendliness", working paper.